142 PECULIAR ORGANIZATIOJfg. 



These examples mark the attention of the Creator to 

 three great kingdoms of his animal creation, and to their 

 constitution as such. The example which stands next in 

 point of generality, belonging to a large tribe of animals, or 

 rather to various species of that tribe, is the poisonous tooth 

 of serpents. 



I. The fang of a viper is a clear and curious example 

 of mechanical contrivance. (Pl.XXlII.fig. 4,5.) It is a per- 

 forated tooth, loose at the root ; in its quiet state lying down 

 flat upon the jaw, but furnished with a muscle^ 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 commu- 

 nicating with the perforation, lies a small bag containing^ 

 the venom. When the fang is raised, the closing of the 

 jaw presses its root against the bag underneath : and the 

 force of this compression sends out the fluid, with a con- 

 siderable 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 1 Yet, though lodged in 

 the mouth, it is so constituted, as, in its inoffensive and 

 quiescent state, not to interfere with the animal's ordinary 

 office of receiving its food. It has been observed, also, 

 that none of the harmless serpents, the black snake, the 

 blind worm, &yC. have these fangs, but teeth of an equal 

 size, not moveable, as this is, but fixed into the jaw, 



II, In being the property of several different species, 

 the preceding example is resembled by that which I shall 

 next mention, which is the hag of the opossum. (PL XXIV. 

 fig. 1,2, 8.) This is a mechanical contrivance, most properly 

 so called. The simplicity 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 easy and constant 

 access to the teats ; in which they are transported by the 

 dam from place to place ; where they are at liberty to run 

 in and out, and where they find a refuge from surprise and 

 danger. It is their cradle, their conveyance, and their 

 asylum. Can the use of this structure be doubted of? Nor 

 is it a mere doubling of the skin, but it is a new organ, 

 fiirnished 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 mus- 

 cles, which serve to open the bag. To these muscles there 



