ON ANIMAL LIFE. 577 



can discover no traces of the manner in which they are produced. The 

 process, by which their numbers are sometimes increased, is no less astonish- 

 ing than their first production ; for several of the genera often appear to 

 divide spontaneously, into two or more parts, which become new and dis- 

 tinct 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 straining 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 in- 

 formed of the qualities of external objects by the senses of touch, taste, 

 smell, hearing, 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 com- 

 pletely 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, denomi- 

 nated 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 masti- 

 cation of the food, which has been received by the mouth. The food thus 

 prepared is conveyed into the stomach by the operation of swallowing ; 

 but in ruminating cattle, it is first lodged in a temporary receptacle, and 

 more completely masticated at leisure. In the stomach, it undergoes 

 digestion, and being afterwards 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 ab- 

 sorbents 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 cir- 

 culation, before they can arrive at the kidneys, by which the superfluous 

 parts are rejected. The chyle passes unaltered, with the blood, through 

 the right auricle and ventricle of the heart, and enters the lungs, to be 

 there more intimately mixed with it, and perhaps to be rendered animal 

 and vital ; while the blood receives from the air, in the same place, a 

 supply of oxygen, with a small portion of nitrogen, and emits some super- 

 fluous carbonic matter, in the form of carbonic acid. The blood, thus 

 rendered arterial, returning to the left side of the heart, is distributed 

 thence to every part of the system, supplying nutriment throughout, 

 while the glands and arteries secrete from it such fluids, as are become 



