22 FUNCTIONS OF ANIMALS AND PLANTS. [iNTROD. 



to the true location of some species. The common sponge, for in- 

 stance, is claimed for each kingdom. 



The various processes by which are effected the ceaseless motion 

 and change, so characteristic of living beings, are called, in physio- 

 logical language, Functions. 



The functions, which are common to all organized beings, have 

 a two-fold object : the preservation of the individual, and the pro- 

 pagation of the species. Those destined for the former purpose are 

 the Nutritive Functions: those for the latter are comprehended 

 under the general title Generation. 



The first step in the nutritive functions of both plants and ani- 

 mals, is to form a fluid, which contains all the elements necessary 

 to nourish the various textures, and to supply materials for the se- 

 cretions. This fluid is, in plants, the sap ; in animals, the blood. 



In both classes of beings a process of absorption precedes the full 

 developement of the nutritive fluid : it is by this means that mate- 

 rial is obtained for its formation. Within the plant or animal it 

 becomes more completely elaborated. 



In plants, the absorption takes place by the spongioles of the 

 roots. A fluid, already prepared in the soil, water, holding in 

 solution carbonic acid and various mineral substances, passes 

 through them into the vegetable organism, without undergoing any 

 reduction or preparation during its transit. In animals, however, 

 the food experiences much change, and a more or less elaborate 

 process of digestion takes place, before a fluid is formed, capable, 

 when absorbed, of furnishing the materials of the blood. 



Plants, fixed by their roots in the soil, imbibe from it their nutri- 

 ment. Animals, obtaining food from various sources, introduce it 

 into a digestive cavity, where it is prepared for absorption. 



The presence of a digestive organ, or stomach, is characteristic 

 of animals. The only instances in which a similar organ may be 

 supposed to exist in the vegetable kingdom, are to be found in those 

 remarkable modifications of leaves, called pitchers (ascidia] in Ne- 

 penthes, Sarracenia, and Dischidia. In the last two plants, these 

 organs certainly serve to retain and dissolve the bodies of insects in 

 the fluid which partially fills them : in Sarracenia, according to Mr. 

 Burnett, the fluid contained in the pitchers is very attractive to in- 

 sects, which, having reached its surface, are prevented from return- 

 ing by the direction of the long bristles that line the cavity. The 

 dissolved food is then absorbed into the plant. 



On the other hand, the animal kingdom affords some exceptions 

 to the presence of a stomach. In such animals, the absorption of 



