. APPLICATION TO METAZOA. 121 



cates a profound difference of constitution between 

 the two groups. The importance of the division, 

 from a morphological point of view, in its bearings 

 on the cell theory, has, I think, led to the assumption 

 of a physiological importance which has no sure foun- 

 dation ; for the assumed difference seems to be based 

 wholly on morphological evidence, whereas what phys- 

 iological evidence may be obtained points to a physi- 

 ological similarity between the two groups. Thus, 

 as nearly as can be ascertained, they have each 

 nearly the same chemical elements for the basis of 

 their composition ; the general phenomena of nutri- 

 tion are the same ; they each alike react to anaes- 

 thetics and various physical and chemical stimuli ; 

 they each 'have the power of separating off a small 

 portion of the substance of their body, and thus 

 reproducing their kind. The prevailing difference 

 which is generally agreed to exist between the two 

 groups is, that in one case the protoplasm composing 

 the body is intersected by the cell walls, running in 

 all directions, while in the other case there seems to 

 be no partition of the protoplasm ; and this continu- 

 ous mass of protoplasm, which composes the entire 

 body of one of the protozoa, is considered as equiva- 

 lent to one of the cells of a metazoon. In the 

 simpler forms of the metazoa, each cell has a nu- 

 cleus ; in the more complex of the protozoa, a single- 



