738 LECTURE LIX. 



parts, which become new and distinct animals, so that in such a case the 

 question respecting the identity of an individual would be very difficult 

 to determine. The volvox, and some of the vorticellae are remarkable for 

 their continual rotatory motion, probably intended for the purpose of strain- 

 ing their food out of the water: while some other species of the vorticella 

 resemble fungi or corallines in miniature. 



Among the animals of these different classes, the more perfect are informed 

 of the qualities of external objects by the senses of touch, taste, smell, hear- 

 ing, and vision. A few quadrupeds are incapable of seeing: the mole has an 

 eye so small as to be with difficulty distinguishable; and the mus typhlus, 

 supposed to be the aspalax of Aristotle, has its eye completely covered by the 

 skin and integuments, without any perforation. Birds have hearing, but no 

 external ears, or auriculae. Insects appear to want the organs of smell; but 

 it is not impossible that their antennae may answer the purpose of hearing. 

 Many of the vermes are totally destitute of sight, and some of all the organs 

 of sense: none of them have either ears or nostrils. The external senses of 

 animals with warm blood are usually liable to a periodical state of inactivity 

 in the night time, denominated sleep. It is said that fishes never sleep; and 

 it is well known that some animals pass the whole of the severest part of the 

 winter in a state nearly resembling their usual sleep. 



In animals which approach, in their economy, to that of the human system, 

 the process for supporting life by nutrition begins with the mastication of the 

 food, which has been received by the mouth- The food thus prepared is con- 

 veyed into the stomach by the operation of swallowing; but in ruminating 

 cattle, it is first lodged in a temporary receptacle, and more completely mas- 

 ticated at leisure. In the stomach, it undergoes digestion, and being af- 

 terwards mixed with the bile and other fluids, poured in by the liver and the 

 neighbouring glands, it becomes fit for affording the chyle, or nutritive juice, 

 which is separated from it by the absorbents of the intestines, in its passage 

 through the convolutions of a canal nearly forty feet in length. Together with 

 the chyle, all the aqueous fluids, which are swallowed, must also be absorbed, 

 and pass through the thoracic duct into the large veins entering the heart, and 

 thence into the general circulation, before they can arrive at the kidneys, by 

 which the superfluous parts are rejected. The chyle passes unaltered, with 



