CHAP, v.] CONSTITUTION OF ORGANISED BODIES. 47 



We are disinclined to admit that this classification, so sharp, 

 so decided, can be admitted in all its inflexible rigour ; but we 

 may accept it as giving a good general view, as grouping under a 

 small number of heads a great variety of vegetal and hisfcological 

 elements. 



3. Histology of Animals. 



The anatomical animal elements differ in general from the 

 vegetal elements in the threefold point of view of chemical 

 composition, of structure, and of form. 



In effect, while in plants the anatomical element is in chief 

 part constituted by a non-azotised ternary substance, the cellulose ; 

 the animal elements, on the contrary, are formed especially by 

 the quaternary albuminoidal substances. No doubt we en- 

 counter in animals ternary substances analogous to the starch 

 and the cellulose of plants, but partially, secondarily, and in 

 small quantity. It is thus that we find in the tegument of the 

 arthropods, and even in all classes of the invertebrates, a matter 

 very analogous to the vegetal cellulose, chitine, which can trans- 

 form itself into glucose. But these points of detail do not 

 weaken the value of the grand general fact enounced above. 



The general differences of structure are perhaps in proportion 

 to the differences of chemical composition. The albuminoidal 

 substances are in effect essentially colloidal, and consequently 

 must tend to a more unfixed morphology. Thus, while in the 

 vegetal cell we generally find an enveloping membrane with the 

 exactest limits, this membrane is often lacking in the anato- 

 mical animal elements. In the latter case the element is a small 

 figurate glomerule, approaching more or less the type fibre or the 

 type cell, and usually furnished with one or more nuclei and 

 nucleoles. 



From the point of view of form, the difference between the 

 histological animal elements and the histological vegetal elements 

 is more marked still. The vegetal histological types are few, 

 and are all related directly and visibly to the cell. But the 



