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In all cases stimulation of a genuine cardiac augmentor causes increase in the work done by the heart, hence these nerves should be called augmentors rather than accelerators.
Application of the Rapidly Interrupted Current to the Heart itself. In addition to the white dots seen at the points of application of the electrodes and the dilation and blue appearance following the use of a weak or moderate current, another effect noticed in the alligator, on the use of a very strong current deserves mention. From the part where the electrodes touched the auricle a considerable area took on a pale, even whitish aspect and seemed to diminish in size; by gradually moving the electrodes along, more and more of the auricle passed into the same condition. The part involved was thrown out of action, as in the case of the dilated portion. This condition seemed to be one of pronounced contraction, probably tetanic, and confirms the view that the white dots seen in all cases just where the electrodes touch are caused by contraction of the muscle fibres.
The Cardiac Rhythm of Fishes and the Action on the same of certain Drugs and Poisons. By T. WESLEY MILLS.
The object of the investigation was (1) to ascertain whether there were considerable physiological differences in the hearts of different fishes, and (2) to ascertain the laws regulating the rhythm of some one fish heart specially suitable for investigation, and (3) to determine the action of certain drugs and poisons on the fish's heart; these being, many of them, such as have been studied in their influence on the heart of the frog.
In general it may be said that the hearts of fishes are so sensitive to changes in normal conditions, and that most fishes are so easily killed, that it is not possible to pursue prolonged investigations on their hearts in situ. This remark applies especially to the Selachians whose hearts, from many points of view are exceedingly interesting.
Batrachus Tau (toadfish), is a fish of great vitality, resisting unfavorable conditions admirably, and its heart has a corresponding vital resistance, and being excellently suited for experimentation, this fish was the subject of a majority of the experiments of this investigation. Most of the work was done on the heart in situ, but the isolated heart was also studied. For the former experiments the fish was kept on its dorsal surface in a dish of water, the latter reaching sufficiently high to cover the gills but not flow over the exposed heart. The respirating centre was left intact. Under these circumstances the heart may be maintained fairly normal for several hours.
Considerable differences in physiological behavior have been found in the hearts of fishes, some of which will be noticed under different headings in this synopsis.
The Structure and Action of the Fish's Heart. In the Selachians, as examined by the present writer in the shark and skate, the heart consists of a Conus arteriosus, in addition to the sinus, auricle and ventricle. This structure is pulsatile and seems to be the most sensitive part of the whole heart. The corresponding Bulbus arteriosus of other fishes is highly elastic but not pulsatile.
In observing such a heart as that of Batrachus during systole of the ventricle, the longitudinal and transverse diameters of the latter are seen to be shortened and the antero-posterior lengthened. It is seen that the apex ascends and the bulbus descends.
In the Selachians the beat is more highly peristaltic than in the hearts of other fishes, and in the former a reversal of the order of pulsation for the different parts is most easily originated and maintained.
In some fishes, as in the eel (McWilliam) and Batrachus, there is a part of the heart intermediate between the sinus and the auricle proper, as to appearance, structure, and functions; and, as it is in most respects physiologically like a corresponding part in the Chelonians, has been named by me sinus extension in both fishes and Chelonians ("basal" wall, and "flattened" portion of Gaskell, "Canalis Auricularis" of McWilliam). This part of the heart is often under peculiar circumstances in action when the auricle proper is quiescent, and then serves to conduct the wave of contraction on from the sinus to the ventricle.
Influences Affecting the Natural Rhythm of the Heart. Among these, in addition to mechanical excitation inducing a reversed rhythm already
referred to, must be especially mentioned the condition of the blood supplying the heart as to degree of oxidation. Blood poor in oxygen, with greater readiness than in other cold-blooded animals, causes irregularity or arrest of the heart in the fish.
Faradisation of the heart in the fish leads to results very closely allied to those obtained in the Chelonians.
Reflex Cardiac Inhibition. The ease with which the heart of the fish can be reflexly inhibited by the stimulation of various parts of its body is one of the most remarkable facts brought out by investigation on the heart physiology of this animal.
The results are much the same whether mechanical or electrical stimulation with the rapidly interrupted current be employed. The parts that have been found most effective in Batrachus are the gills, the air bladder, the abdominal viscera, the mucous lining of the mouth, the tentacular appendages of the mouth, the pectoral fins, the anus and the tail.
The results may be either (1) decided arrest of the heart for several seconds, followed by a slowed rhythm, or (2) brief arrest with slowed and irregular rhythm or (3) the latter lasting from one to two minutes or longer without any actual stop of the heart. In some cases the operative procedure necessary to expose the heart is sufficient stimulus to keep the heart long inhibited. The after results of inhibition are not uniform. In some cases no acceleration seems to follow, but in others and the majority there is decided acceleration of the rhythm.
Peculiar Results associated with Reflex Cardiac Inhibition. Stimulation of several of the parts mentioned above, and especially of the anus and tail, have given the following remarkable results:
(1.) At first an accelerated rhythm followed by a slowed rhythm, or (2.) An accelerated rhythm followed by a slowed rhythm on increasing the current, or
(3.) Only an accelerated rhythm.
This subject is further treated in the account of the turtle and alligator above.
It should be noted that in the skate, stimulation along certain lines on the ventral surface of the fish, apparently the course of mucous glands and likely associated with special sensitive structures, has produced remarkably good cardiac inhibition, and the results have been constant. The mucous membrane of the mouth is also, in the skate, a part giving decided results.
Independent Rhythm of Various Parts of the Heart. A large number of experiments on both the isolated heart and the heart in situ have brought out the following facts:
(1.) There is very great variety in the hearts of different fishes as to capacity for independent rhythm; between such fishes as the skate, the shark, and the toadfish (Batrachus) this difference is enormous.
(2.) In Batrachus every part of the heart is capable of good, independent rhythm; even the apex of the heart when isolated has shown such. (3.) The order of the parts of the heart with greatest independent rhythmic power is--sinus, sinus extension, auricle, ventricle.
(4.) The independent rhythm of the ventricle begins soon after its separation from the rest of the heart (by ligature), speedily reaches a maximum and gradually declines.
The Action of Certain Drugs and Poisons on the Heart. Experiments have been made on the heart in situ and the results confirmed on the isolated heart. The agent was in each case applied in solution directly to the heart itself. The results are below stated very briefly.
Pilocarpin and Atropin in one per cent. solution. (1) These agents are antagonistic in action. (2) Pilocarpin is a cardiac depressant; atropin an excitant; the former lowers cardiac excitability; the latter most decidedly heightens it; the former weakens the beat and tends to arrest the heart in diastole, the latter calls into action the resources of the heart quickly and fully. Sodium and Potassium Carbonate in five per cent. solution. These agents are antagonistic in action. Sodium carbonate is a cardiac excitant, potassium carbonate a depressant. The former tends to quicken the beats and diminish diastole. A heart arrested in diastole by potassium carbonate may be excited to action by sodium carbonate. Potassium carbonate must be regarded as a cardiac poison.
Lactic Acid. (1) In five per cent. solution this is a rapid cardiac poison. (2) In one per cent. solution its action is slower but it proves a decided depressant and the heart arrested by lactic acid cannot be excited to action by digitalis, sodium carbonate, &c.
Nicotin in one per cent. solution. (1) Its first action was often to arrest the heart in diastole. (2) This was sometimes followed by an irregular slowed rhythm giving way to a more rapid but weaker heart beat. But the fish heart shows great power of resistance against the effect of nicotin in weak solution and can, it would seem, recover almost wholly from the effect of this poison. Nicotin tends strongly to produce incoördination of the beat.
Chloroform (undiluted) acts as a decided cardiac depressant, tending to arrest the heart in diastole. The heart can, however, recover fairly well from a considerable quantity of this poison applied directly to it.
Acetate of Strychnia in one per cent. solution. This poison did not seem to have the most pronounced action, but tended to strengthen the systole, diminish diastole and arrest the heart in systole.
Veratria in rather less than one per cent. solution. The most distinct action is on the diastole, which it retards. The heart in action has a generally sluggish movement rather than a weakened one; the systole may in fact be slightly improved. It also tends to cause arhythmic phenomena -want of harmony in the sequence of the beats of different parts and of different fibres in the same part, e. g., there may be two or more beats of the auricle for one of the ventricle, &c., or one part of the ventricle may be pulsating out of harmony with the rest.
Digitalin in somewhat less than one per cent. solution. This has more than any other of the agents tested a constant, decided and well defined action. (1) A short time elapses before its action is manifested; but when this begins it quickly and steadily rises to a maximum. (2) It causes diminished diastolic relaxation; but especially characteristic is the effect on the systole which is both more perfect and when complete more prolonged than usual. (3) The ventricle is always arrested in most pronounced (tetanic?) systole and then always looks very small and pale. It is inexcitable.
The action of drugs on such sensitive hearts as those of the Selachians was found correspondingly rapid. The action on the isolated heart was also more rapid than in the heart in situ, as was to be expected.
In many cases the first effect of a drug was to arrest the auricle proper leaving the sinus extension comparatively unaffected.
Origin of the Endoderm in Lepidoptera. By A. T. BRUCE.
A tolerably complete series of sections of Thyridopteryx at different stages of development, prepared at the biological laboratory of the University, has thrown considerable light on the embryology of the Lepidoptera.
In the earliest stages studied, the eggs were already segmented, consisting of a superficial blastoderm of flattened roughly hexagonal cells enclosing a segmented yolk. The central or yolk cells have large granular nuclei scantily invested with protoplasm which, sending out long filaments, encloses a number of yolk spherules, consequently each yolk cell is a centre of attraction to the spherules surrounding it. It is the adhesion of these spherules to the peripheral filaments of the yolk cells which causes the segmentation of the yolk (Figs. I and II). Adjacent yolk cells appear in some sections to be united by filaments, while the superficial yolk cells are, at times, connected with the blastoderm. Moreover the yolk cells are apparently connected with the amnion covering the embryo, consequently the entire egg may, perhaps, be regarded as a protoplasmic continuum. The embryo with the amnion in all probability originated as a thickening of the blastoderm, which, sinking into the yolk, formed the floor of a pit or invagination. The walls of this invagination then grew together and united above the floor. Consequently the embryo forming the floor of the invagination and the amnion forming the walls of the same were constricted off from the rest of the blastoderm and sinking deeper into the yolk came to lie near the centre of the egg. I have observed the stages of this process in Mantis, and in Thyridopteryx it is probably quite similar.
The embryo in the earliest stages examined was watch-glass shaped, with its convexity covered by the amnion. The latter consists of flattened branched cells with large nuclei. The embryo at this stage is a syncitium, thickly studded with nuclei, frequently in process of division. Later, a thickening extends along the major axis of the embryo on its concave side. At the same time a shallow groove is formed along the major axis on the
convex side of the embryo (Fig. 1). At this time the embryo has increased in length and become pear-shaped, the broad anterior end comprising the procephalic lobes. Metameric segmentation has commenced, successive somites being separated by incisions of the ectoderm. The mass of cells lying under the groove becomes separated by incisions from the outer layer. The process of separation is commencing in Fig. I. The mass of cells thus separated extends laterally on each side and ultimately forms a second layer lying beneath the outer ectoderm. The groove from the thickened floor, of which the inner layer is separated, may fairly be regarded as a blastopore, and has been described as such in the figures referred to. After the inner layer has been formed it separates into two bands. The point where the separation occurs is immediately beneath the blastopore. An ingrowth of cells then occurs at the blastopore and extends between the two bands of the inner layer. This ingrowth gives rise to the clear migratory cells, larger than the other cells of the embryo (Fig. II). At the same time the ectoderm lying near the lips of the blastopore thickens. It then separates into superficial and deeper portions. The latter gives rise to the ganglia of the nervous system (n. 8., Fig. II). The amnion then extends dorsally more rapidly than the body walls until the folds of the opposite sides unite (P', Fig. II). By the union of the amniotic folds of opposite sides the embryo comes to lie free in a hollow sock of amnion. The dorsal wall of the embryo is formed by the union of the inner limbs of the amniotic folds. A portion of the inner germ layer then grows round and finally encloses the yolk taken into the body cavity by the union of the amniotic folds.
The cells of the inner layer which surround the yolk from the epithelium of the mid gut and consequently are to be regarded as endoderm cells. The large yolk cells apparently take no part in the formation of the latter. The fore and hind guts are formed as invaginations of the ectoderm before the formation of the mid gut. The latter arises from the last abdominal somite, the former, just behind the procephalic lobes. The tracheae and limbs arise in the customary manner. That portion of the inner layer lining, the limbs, and body cavity is to be regarded as mesoderm. In late embryonic life most of the mesoderm appears to be converted into clear migratory cells. The nervous system arises as independent ganglia. The sub-œsophageal ganglion is formed by the union of the two maxillary with a portion of the mandibular ganglion. The last or tenth abdominal somite has a small ganglion.
Concerning the origin of the endoderm there has been considerable uncertainty. Balfour, speaking of the origin of the endoderm, says: "The origin of the hypoblast is still in dispute." Kowalevsky, as interpreted by Balfour, described the origin of the endoderm from the inner layer. Tichomeroff, from observations on silk worms, inclines to the same opinion. Dohrn, however, does not agree with Kowalevsky, while Balfour thinks that the endoderm may be formed from the central yolk cells. The numerous sections in my possession leave little doubt that the endoderm is formed from a portion of the inner layer which arises at the floor of the germinal groove or blastopore. The embryo of Thyridopteryx may then be fairly described as possessing a gastrula stage. Space does not permit references to literature. bl. Fig. 2.
On the Artificial Propagation and Cultivation of Oysters in Floats. By W. K. BROOKS.
Without expressing any opinion as to the value of the process of “fattening" oysters by placing them for a few days in cars floating in fresh water, I wish to point out that there is no similarity between this process and the process of propagation which is here described.
My attention was first called to the value of floating cars in oyster culture by Mr. William Armstrong, of Hampton, Virginia, who informed me, in 1884, that "seed" oysters, which he had placed in floating cars in the mouth of Hampton creek, grew more rapidly, and were of a better shape and more marketable than those which grew from seed planted on the bottom in the usual way.
One of the results of my study, in 1879, of the development of the oyster was the discovery that there is a period of several hours, immediately after the embryo acquires its locomotor cilia, when it swims at the surface, and this is the period when it is swept into contact with collectors. As soon as the shell appears the larva is dragged down by its weight, and either settles to the bottom and dies, or swims for a time near the bottom. The tendency to swim at the surface is an adaptation for securing wide distribution by means of the winds and currents which sweep the young oysters against solid bodies which may serve for attachment, and the greatest danger to which the oyster is exposed, at any part of its life, is that it may not, at the swimming stage, find a clean hard surface for attachment.
As it is microscopic and only about half as thick as a sheet of thin paper, it may be smothered by a deposit of sediment or mud so light as to be invisible, and most of the failures to get a good "set of spat" are due to the formation of a coat of sediment upon the collectors before the young oysters come into contact with them.
It occurred to me this summer that this danger could be entirely avoided by the use of floating collectors, for little sediment can fall on a body which is close to the surface of the water, and most of this will be swept away by currents, which will, at the same time, sweep the swimming embryos down into the collector, and thus insure an early, abundant and successful “set.”
I accordingly constructed a floating car, made so as to permit the free circulation of the water. This was filled with clean oyster shells and moored in the channel in front of the laboratory at Beaufort, N. C., on July 4th. As all the oysters in the vicinity were in very shallow water they were nearly through spawning, and the conditions were therefore very unfavorable; but notwithstanding this, I immediately secured a good "set" and the young oysters grew with remarkable rapidity, on account of the abundant supply of food and fresh water which gained ready access to all of them, and the uniform temperature which was secured by the constant change of
This method of oyster culture may be applied in many ways; of which the most obvious is the production of seed oysters for planting.
The seed which is used for planting in Maryland and Virginia, as well as in Delaware and further north, is now procured from the natural beds of our waters, by tonging or dredging, and as the demand for oysters for this purpose is certainly one of the elements which have led to the depletion of our beds, there is a wide-spread feeling that the exportation of "seed" should be prohibited.
By a small investment of capital in floating collectors any one on tidewater could easily raise large quantities of much better, cleaner seed than that which is now procured from the natural beds, and if the laws permitted the sale and transportation of this seed without restriction at the season when the demand exists, it could be sold at a profit for less than the cost of tonging.
Northern planters could also raise seed for themselves by constructing floating collectors in the warm water of the sounds of Virginia and North Carolina, where the length of the summer would permit several collections to be made in one season. The oysters thus reared are large enough for planting in five or six weeks, and in the latitude of Beaufort there is an abundance of spat from the middle of April to the first of July, and it can be collected until September.
The method may also be used by planters for collecting their own seed, especially in regions remote from a natural supply. If there are no oysters near to furnish the eggs, a few spawning oysters may be placed among the shells in the collector, after the French method, to supply the "set."
It can also be used for the direct production of marketable oysters especially over muddy bottoms, and in regions where public sentiment does not permit any private ownership of the bottom.
As food for the oyster is most abundant at the mouths of muddy creeks where the bottom is too soft for oyster culture by planting or by shelling, this method will have especial advantage in such places, for there will be no danger of sanding or of smothering by mud at the surface, and there is no limit to the number of oysters which can thus be grown on a given area, for the free current of water will bring food to all of them.
The very rapid growth will more than compensate for the cost of the floats, and Mr. Armstrong's experiment shows that, in addition to all these advantages, the oysters are of a better shape, with better shells, and more marketable than those grown at the same place on the bottom.
Finally this method will do away with the necessity for a title to the bottom, and will thus enable a few enterprising men to set the example of oyster culture, and by the education of the community, to hasten the time when wiser laws will render our natural advantages available for the benefit of our people.
The most economical method of constructing floats must, of course, be determined by practical experiments, but a float constructed by connecting two old ship-masts together by string pieces, with a bottom of coarse galvanized iron netting, would have sufficient buoyancy and enough resistance to water to support a large quantity of submerged shells and oysters for two or more seasons, and a coating of copper paint each year would protect the timbers from worms.
The floats should be open at the ends to permit free circulation, and they should be moored in such a way as to swing with the current.
Engagement in business projects is no part of the office of a university, and I feel that the experiments of the past summer have brought the subject of oyster culture to a point where its further development should be left to the people who are most interested.
Two species of Stomatopoda are common at Beaufort; Squilla empusa, and a Lysiosquilla which, so far as I am aware, has never been described. The swimming larvae of both species are very abundant, but I have not succeeded in obtaining the eggs, nor was I able to keep the younger larvae alive in confinement, as they all died in moulting, although the older larvae moulted in aquaria. I was therefore compelled to rely upon general resemblances and measurements in my attempts to trace the metamorphosis, although the series were so complete that I believe my results are worthy of confidence. The youngest Lysiosquilla larvae were in the same stage as Claus' larva. This stage is followed by an Erichthus stage, which persists for a number of moults, with little change except the increase in size and the gradual acquisition of the appendages.
I have witnessed the change from the last form of this series into the young Lysiosquilla, so it is now certain that the Erichthus type is the larva of this genus, although it is of course possible that other genera may pass through the same larval stages.
As secondary sexual characters are rare among the higher Crustacea, it is interesting to note that the female Lysiosquilla is much larger than the male, and of quite a different color. Fully grown males are from one and a half to two inches in length, while the females are from three to four inches long. The males are of a gray color and quite transparent, while the females are more opaque and of a dark olive green color, nearly black.
The habits of our two species are quite different. Lysiosquilla lives in pure sea sand on beaches which are directly exposed to the ocean swell, and it is very abundant on Bird Shoal and on the sea beach at Fort Macon. It lives in a deep cylindrical vertical burrow, which goes down for several feet, and it is almost impossible to procure the animals by digging. The males and females inhabit different burrows, and they lie in wait for prey at the top, which is arched over with sand, so that only the eyes of the animal are exposed. When suitable prey comes within reach they dart out so quickly that the eye can scarcely follow the motion, and seizing the prey in the large claws, they instantly retreat to the bottom of the burrow, where the food is stored away, and the animal returns to the mouth of the burrow to resume its watch. They seldom venture more than three or four inches from the
burrow, and I have obtained only one specimen which was captured in the water, although the trawl often brings up an abundant supply of the much larger Squilla empusa.
In constructing its burrow, Lysiosquilla brings up the sand from the bottom by armfuls, which are carried between the large claws to the mouth of the hole, to be deposited as far away as the animal can reach without leaving its burrow.
The burrows are so deep that digging for the animals is almost useless, and after many unsuccessful attempts to trap them, I found that it was easy to catch them by holding a piece of fish or crab near the mouth of the burrow as a bait, with one hand, while the other hand was held ready to cut off the retreat into the burrow, by the use of a tin trowel. Their movements are so very quick that many escaped entirely, while others were cut in two by the trowel, although many were captured alive.
Squilla empusa lives in hard muddy bottom, in or on the sides of channels where there is a rapid current, and it constructs a shallow U-shaped burrow, open at both ends. The burrow is excavated by the current of water produced by the abdominal appendages, and I have never seen them carrying sand out of the holes. They do not arch over the opening, and they are often found swimming at a distance of many feet from the hole, probably in pursuit of prey.
Squilla stridulates, by rubbing the serrated spine of the swimmeret across the serrated ridge on the ventral surface of the telson. The noise which is thus made under water can be clearly heard above the surface.
Note on the Fishes of Beaufort Harbor, N. C. By O. P. JENKINS.
In the Proceedings of the U. S. National Museum, 1878, is published a list of the fishes of Beaufort Harbor, N. C., by Profs. Jordan and Gilbert.
This list includes both the fishes observed by Drs. Coues and Yarrow, and published by Dr. Yarrow in the Proceedings of the Philadelphia Academy of Natural Sciences for 1877, and those added by the work of Profs. Jordan and Gilbert. During the past summer while attending the session of the Marine Laboratory I made a collection of the fishes of the harbor. Among the number obtained the following twenty species do not occur in either of the lists referred to. Several of the number are here for the first time recorded at a point on our coast so far north. The fishes of this collection have been placed in the Museum of the Indiana State University. Dr. Jordan has had the kindness to examine the collection, and has identified the species in this list.
A NOTE ON INHERITANCE.-Including a letter from Fritz Müller.
BY W. K. BROOKS.
In a recent article in the Jenaische Zeitschrift für Naturwissenschaft. (Bd. xviii, N. F. xi), Dr. Düsing briefly discusses my view of the nature of inheritance, as set forth in my book on "Heredity," and while he seems to be greatly disposed to accept my views on the whole, he points out certain difficulties which suggest themselves to him, and which seem to me to be the result of a failure to completely catch my meaning, but as other writers besides Dr. Düsing have called my attention to the same points, I am forced to believe that I have failed to express myself clearly.
Thus he says, p. 457: “Indessen scheint es mir, als ob Brooks in der Annahme, dass das Weibchen überhaupt gar nicht variire, zu weit gegangen wäre. Wenn es auch nicht unmöglich ist, so scheint es doch ausserordentlich unwahrscheinlich zu sein, dass die Geschlechtscharacter des Weibchens, z. B. die Milchdrüsen der Säugetiere, zuerst beim männlichen Geschlecht aufgetreten seien. Wenn die Weibchen gar nicht variirten, so hätte auch die weitere Ausbildung der Milchdrüsen zuerst bei den Männchen stattfinden müssen, bei denen sie später erst wieder reduciert worden wären. Weit einfacher ist es, bei der bisher allgemein gültigen Ansicht zu bleiben, dass das Weibchen ebenfalls variirt-allerdings in weit geringerem Masse, als das Männchen.
"Der beste Beweis für die Variabilität des weiblichen Geschlechtes zeigt sich bei der parthenogenetischen Fortpflanzung. Bei den Daphniden z. B. haben die parthenogenetischen Weibchen neue Eigenschaften erworben, welche sie von den Geschlechtsweibchen unterscheiden; sie sind z. B. nicht mehr befruchtungsfähig. Diese Eigenschaft können sie erst später erlangt haben, als sie bereits ungeschlechtlich producierte Jungfernweibchen waren, an einen männlichen Ursprung kann nicht gedacht werden. Es ist dies ein sicherer Beweis, dass auch die ungeschlechtlich producierten Weibchen variiren.
"Obgleich Brooks in seinem Werke auf die Möglichkeit eines männlichen Ursprunges der weiblichen Geschlechtscharactere hingewiesen hat, (Heredity, p. 240), so scheint er doch seine Meinung schon berichtigt zu
haben, da er in dem oben stehenden Aufsatze (Ueber ein neues Gesetz der Variation von W. K. Brooks, Jen. Zeit., xi. 452), unter 6 zugiebt, dass auch das Weibchen variiren kann, wenn auch seine Variation im allgemeinen nicht so stark ist, als die des Männchens."
If it were true that I have found it necessary to make such an essential change in my hypothesis less than two years after publication I should assuredly feel guilty of hasty publication of crude thoughts, but I think that a reference to the page of "Heredity" to which Dr. Düsing alludes will show that the statement in my own recent paper is not an amendment or a correction in any sense, and that the possibility of female variation is definitely set forth in the book on Heredity.
Page 240 opens with the following sentence: "We must recollect that our hypothesis does not demand that the power to transmit variations should be confined exclusively to males, but simply that it should be more active in them than it is in the females"; and on page 241: "The remarkable instinct which leads some species of cuckoos and crow-black birds to lay their eggs in the nests of other species must have originated in females, and a collection of all the cases which must be explained in the same way would make a formidable list; but the fact would still remain, that among animals with separate sexes such modifications are very much more frequent than female modifications, and this is all that our theory requires."
These expressions seemed to me, when I wrote them, as they still seem to me, to recognize the possibility of female variation with as much definiteness as my statement on p. 435 of the Jenaische Zeitschrift, that "Eine Variation, welche zuerst in einem Männchen erscheint, hat viel mehr Wahrscheinlichkeit erblich zu werden als eine solche, welche zuerst in einem Weibchen erscheint."
The view which I have sought to express is that the functions of the two reproductive elements were originally alike, and that the ovum has gradually become specialized for transmitting the hereditary characteristics of the race, while the male element has gradually lost much of this power, and
JOHNS HOPKINS UNIVERSITY CIRCULARS.
has become specialized for the production of variations, while the ovum has gradually lost much of the power to excite variability. I do not assert, however, that this specialization is complete, and that the male cell has no power whatever to transmit hereditary characters, and the ovum no power to transmit variability, but simply that the two elements have become modified in their two divergent directions, and it seems to me that this fact will furnish a solution for another of Düsing's difficulties. On page 460 he says: "Die Eigenschaften, wodurch sich die Menschen von einander unterscheiden, sind Variationen oder Eigenschaften, die erst kurz vorher erworben wurden. Diese - es sind die, worauf man am meisten achtet — muss der Mann vererben, es muss also das Kind in seinen Eigenthümlichkeiten dem Vater gleichen — oder wenigstens durchschnittlich dem Vater mehr, als der Mutter. Im allgemeinen ist dies schwer zu untersuchen, aber es giebt doch Fälle, die uns Aufschluss geben können. Ein Christ mit hellen Haaren und blauen Augen ist mit einer Jüdin verheiratet; aber die zwei Kinder tragen jüdischen Typus. Wenn nun die Eigenschaften der Juden nicht zu den Grundcharacteren der Species gehören, so geht hieraus hervor, dass im Gegensatze zu der Theorie von BROOKS auch neu erworbene Eigenthümlichkeiten von der Mutter vererbt werden können. Ist die Mutter Negerin, der Vater ein Weisser, so werden stets Mulatten erzeugt. Wenn also die Theorie von BROOKS richtig ist, so müssen auch die Eigenschaften, welche den Neger vom Weissen, den Juden vom Christen unterscheiden, zu den seit sehr langer Zeit erworbenen Eigenschaften gerechnet, als Grundeigenschaften einer besonderen Rasse angesehen werden und daher von der Mutter vererbt werden können.”
A third point which he brings forward involves the most interesting of all the phenomena of heredity; the latent transmission of characteristics, or polymorphic heredity. He says, page 459: "Wenn die Mutter nur die Charactere der Species vererbt, so müssten bei der parthenogenetischen Fortpflanzung immer nur dieselben Tiere wie die Mutter erzeugt werden. Dies aber ist nicht der Fall. Im Ueberfluss werden immer nur JungfernWeibchen geboren d. h. solche, welche ohne Männchen wieder Junge producieren. Sobald aber Mangel eintritt, hört diese starke Vermehrung auf, es werden nicht mehr Jungfernweibchen, sondern befruchtungsfähige Weibchen und Männchen geboren, die also nicht die Eigenschaften der Mutter besitzen. — Indessen könnte man doch darauf hinweisen, dass es sich hier nicht um eine Variation und auch nicht um das Auftreten von neu erworbenen Eigenschaften handelt, sondern dass auch die Eigenschaften dieser Geschlechtsgeneration zu den Grundcharacteren der Species gehören. Die Jungfernweibchen vererben nicht nur ihre eigenen Eigenschaften, sondern auch die Tendenz unter Umständen nämlich im Falle eines Mangels Tiere mit den Eigenschaften der Geschlechtsgeneration zu producieren."
In chapter V, of "Heredity" I have discussed this and similar cases at considerable length, and have tried to show that the explanation which Düsing suggests is the true one. On page 112 I say: "Certain embryo bees, when exposed to certain conditions, develop into sterile workers, but when exposed to another set of conditions they become fertile females. The differences between the workers and the queens are not confined to the reproductive organs, but extend to the shape and size of the body, the general organization, and to the instincts of the animals. These differences are not due to the direct action of the conditions to which the young are exposed, but are truly hereditary, as we see from the fact that the workers of different species are as distinct and as characteristic of their species as the males or the fertile females. . .
"In the case of the polymorphic hydroids an egg-embryo may give rise by budding, to certain descendants with fully developed digestive organs, but with no organs of locomotion or reproductive organs, to other descendants with organs of locomotion, but without digestive organs or reproductive organs, and to still others with reproductive organs but with no organs of digestion or locomotion.
"All these forms are hereditary and are characteristic of the species, so there is no escape from the conclusion that they are all present in some form in the egg-embryo. . . .
"The hypothesis that the egg embryo inherits and transmits to each of its descendants, those produced asexually as well as those produced sexually, all the characteristics of the species, and that it also inherits and transmits to each of them a tendency to suppress certain of these characteristics under certain conditions seems to furnish a simple and satisfactory explanation of all the facts. According to this view the feeding zooids of a polymorphic siphonophore are individuals which have inherited in full all the characteristics of the race, but which do not attain to perfect development in all respects. The swimming zooids are similar individuals, with other characteristics suppressed, and so on.”
If this is the true view it is plain that the variation of zooids formed by budding, or that of animals which are borne parthenogenetically, does not differ essentially from that of animals born from sexual union, except that we must search for the origin of the tendency to vary in remote sexual ancestors, instead of in the parents.
The fact that polymorphic members of a community do inherit all the characteristics of the species, is shown, with remarkable clearness, in the following interesting letter which I received a few days ago from Fritz Müller:
BLUMENAU, SANTA CATHARINA, BRAZIL, July 28, 1885. Hochgeehrter Herr :
Bei dem Interesse, welches die Frage der Vererbung für Sie hat, darf ich mir wohl erlauben, Sie auf eine eigenthümliche Weise der Vererbung aufmerksam zu machen, die bei unseren Meliponen sich findet. Wie mir ein jüngerer Freund (M. Sagemehl in Amsterdam) schreibt, kann nach dem Baue des Kopfes und Thorax, auf den ja auch Packard besonderes Gewicht legt, kaum ein Zweifel sein, dass diese stachellosen Honigbienen (Melipona und Trigona) die nächsten Verwandten von Apis sind. Auch in ihrer Fortpflanzung stimmen sie insofern mit Apis überein, dass die fruchtbaren Weibchen (Königinnen) Kürzere, die Männchen (Drohnen) längere Zeit zu ihrer Entwicklung bedürfen, als die unfruchtbaren Weibchen (Arbeiter). Man darf also wohl annehmen, dass auch bei ihnen, wie bei Apis und anderen geselligen Hymenopteren die Weibchen (Königin und Arbeiter) aus befruchteten, die Männchen aus unbefruchteten Eiern sich entwickeln. Nun sind bei den vier hiesigen Melipona-arten, von denen ich alle drei Formen (♂, und g) kenne, die fruchtbaren Weibchen einander so ähnlich, dass die der drei grösseren Arten nur nach sorgfältigster Untersuchung, die der vierten, weit kleineren, auch fast nur durch ihre geringere Grösse zu unterscheiden sind. Die Männchen dagegen sind überaus verschieden sowohl von ihren eigenen Weibchen, als unter sich. Soweit hat der Fall nichts Ungewöhnliches, denn Ähnliches kommt ja auch bei vielen anderen Insecten vor. Aber,- -und das ist das Merkwürdige, die unfructbaren Weibchen oder Arbeiter gleichen nicht den fruchtbaren Weibchen, sondern den Männchen; sie sind diesen in Grösse, in Farbe, kurz in Allem so ähnlich, dass sie kaum durch die 12 gliedrigen (bei den † 13 gliedrigen) Fühler, durch die ungespaltenen (bei den ở gespaltenen) Fussklauen und durch die Sammelkörbchen der Hinterschienen von ihnen sich unterschieden.
Auch abgesehen von den Arbeitern, ist es bemerkenswerth dass unter den Kindern der Königin die ohne Zuthun eines Mänchens erzeugten, vaterlosen Söhne nicht der Mutter, sondern dem Grossvater, dagegen die aus der Vereinigung mit einem Männchen hervorgegangenen fruchtbaren Töchter der Mutter gleichen.
Eine Beschreibung der vier Melipona-arten finden Sie in "Kosmos," Bd. III, 1878, pag. 228. Vielleicht können Sie den Fall für Ihre Theorie der Vererbung verwerthen.
Mit hochtachungsvollem Grusse,