DISTINCTIVE CHARACTERS OP ANIMALS. 27 



stomach, being extemporized, as it were, on each occasion that 

 aliment is ingested ; and an anal orifice being extemporized 

 in like manner, when the indigestible residue has to be cast 

 forth. All true Animalcules ( 133) have a proper mouth, 

 into which food is drawn by the current created by the cilia 

 ( 45) wherewith it is fringed ; and this mouth leads to the 

 general cavity of the body, within which the food is subjected 

 to the digestive process. In Zoophytes ( 121) which possess 

 a proper stomach, this organ forms so large a part of the 

 animal, that its entire body may be almost said to consist of 

 the stomach and of the prehensile appendages by which it 

 draws in its food. But in all the higher tribes, the stomach, 

 with the alimentary canal proceeding from it, are suspended 

 freely within the general cavity of the body ; and we shall 

 find that the space that surrounds these viscera is extremely 

 important in the economy of all but vertebrated animals, as 

 being a sort of reservoir into which the nutrient materials 

 prepared by the digestive process first transude, and from 

 which it is carried into the remoter parts of the system. In 

 vertebrated animals, this cavity called in them the peritoneal 

 cavity, from its being lined with a serous membrane ( 28), 

 termed the peritoneum *is not subservient to the same pur- 

 poses ; the nutrient materials being taken up from the walls 

 of the digestive cavity, both by. the blood-vessels and by 

 special absorbents, and being by them carried into the current 

 of the circulation. It is obvious that until they have found 

 their way, through one or other of these channels, into the 

 general system, the nutrient materials introduced as food into 

 the stomach of an animal are not within its body, properly so 

 called, any more than a fluid is within a plant when it bathes 

 the exterior of its roots, or within an entozoon when in con- 

 tact with the soft surface of its integument. In each case, 

 the absorption of the fluid is first requisite ; and it is with 

 this that its application to the requirements of the living 

 body really commences. 



9. But further, when we compare together, not the lowest, 

 but the highest members of the Vegetable and Animal king- 

 doms respectively those in which their respective attributes 

 are most characteristically displayed, we find that they 

 present such differences as to render it quite impossible to 

 confound the one with the other. Although it is easy even 



