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It would be very worthy of enquiry, if it were possible to discover, by what method an animal, which lives conftantly in water, is able to fupply a repofitory of air. The expedient, whatever it be, forms part, and perhaps the most curious part, of the provifion. Nothing fimilar to the air bladder is found in land animals; and a life in the water has no natural tendency to produce a bag of air. Nothing can be further from an acquired organization than this is.

THESE examples mark the attention of the Creator to three great kingdoms of his animal creation, and to their conftitution as fuch. The example which stands next in point of generality, belonging to a large tribe of animals, or rather to various fpecies of that tribe, is the poisonous tooth of ferpents.

I. The fang of a viper is a clear and curious example of mechanical contrivance. It is a perforated tooth, loofe at the root; in its quiet ftate lying down flat upon the jaw, but furnished with a mufcle, which, with a jerk, and by the pluck as it were of a string, suddenly erects it. Under the tooth, close to its root, and communicating with the perforation, lies a fmall bag containing the venom.

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When the fang is raifed, the closing of the jaw preffes its root against the bag underneath; and the force of this compreffion sends out the fluid, and with a confiderable impetus, through the tube in the middle of the tooth. What more unequivocal or effectual apparatus could be devised, for the double purpose of at once inflicting the wound and injecting the poison? Yet, though lodged in the mouth, it is fo constituted, as, in its inoffenfive and quiescent ftate, not to interfere with the animal's ordinary office of receiving its food. It has been obferved alfo, that none of the harmless ferpents, the black fnake, the blind worm, &c. have these fangs, but teeth of an equal fize; not moveable, as this is, but fixed into the jaw.

II. In being the property of feveral different fpecies, the preceding example is resembled by that which I fhall next mention, which is the bag of the opoffum. This is a mechanical contrivance, moft properly fo called. The fimplicity of the expedient renders the contrivance more obvious than many others; and, by no means, less certain. A false skin under the belly of the animal, forms a pouch, into which the young litter are re

ceived at their birth; where they have an eafy and constant access to the teats; in which they are tranfported by the dam from place to place; where they are at liberty to run in and out, and where they find a refuge from furprife and danger. It is their cradle, their conveyance, and their afylum. Can the use of this ftructure be doubted of?

Nor is it a mere doubling of the fkin, but it is a new organ, furnished with bones and muscles of

its own. Two bones are placed before the os pubis, and joined to that bone as their base. These support, and give a fixture to, the mufcles, which ferve to open the bag. To these muscles there are antagonists, which serve in the fame manner to fhut it: and this office they perform so exactly, that, in the living animal, the opening can scarcely be discerned, except when the fides are forcibly drawn asunder *. Is there any action in this part of the animal, any procefs arifing from that action, by which these members could be formed? any account to be given of the formation, except defign?

III. As a particularity, yet appertaining to

*Goldfmith's Nat. Hift. vol. iv. p. 244.

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more fpecies than one; and alfo as ftrictly mechanical; we may notice a circumftance in the ftructure of the claws of certain birds. The middle claw of the heron and cormorant is toothed and notched like a faw. birds are great fishers, and these notches affift them in holding their flippery prey. The ufe is evident; but the ftructure fuch, as cannot at all be accounted for by the effort of the animal, or the exercife of the part. Some other fishing birds have these notches in their bills; and for the fame purpose. The gannet, or Soland goofe, has the tide of its bill irregularly jagged, that it may hold its prey the fafter. Nor can the ftructure in this, more than in the former cafe, arife from the manner of employing the part. The smooth furfaces, and foft flesh of fish, were less likely to notch the bills of birds, than the hard bodies. upon which many other fpecies feed.

We now come to particularities strictly fo called, as being limited to a single species of animal. Of these I shall take one from a quadruped, and one from a bird.

I. The ftomach of the camel is well known to retain large quantities of water, and to retain it unchanged for a confiderable length of

time. This property qualifies it for living in the defart. Let us fee therefore what is the internal organization, upon which a faculty, fo rare and fo beneficial, depends. A number of diftinct facs or bags (in a dromedary thirty of these have been counted) are obferved to lie between the membranes of the fecond stomach, and to open into the ftomach near the top by small square apertures. Through these orifices, after the stomach is full, the annexed bags are filled from it. And the water, fo depofited, is, in the first place, not liable to pass into the intestines; in the fecond place, is kept feparate from the folid aliment; and, in the third place, is out of the reach of the digeftive action of the ftomach, or of mixture with the gastric juice. It appears probable, or rather certain, that the animal, by the conformation of its muscles, poffeffes the power of fqueezing back this water from the adjacent bags into the ftomach, whenever thirst excites it to put this power in action.

II. The tongue of the woodpecker, is one of those fingularities, which nature presents us with, when a fingular purpose is to be an fwered. It is a particular inftrument for a particular

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