26 A PRIMER OF BIOLOGY 



Vaucheria or the adult Amoeba or (save for the wall 

 and chlorophyll) Pleurococcus. By division of the 

 original cell there arises a multicellular body which, 

 because it is a primary stage on the w r ay to something 

 higher, we term an embryo. But such an embryo 

 as that shown in Fig. 8 B, is composed of cells which 

 are, speaking generally, similar to each other. Later 

 on, these cells begin to differentiate, begin, in other 

 words, to specialise both in structure and in function, 

 and this differentiation is gradually carried to com- 

 pletion as the adult stage is approached. 



We have thus sketched out in the life-history of 

 the individual the same general advance that we see 

 illustrated in successively higher groups of organisms, 

 so that, in general terms at least, we may say that, 

 assuming for the moment that organisms are genea- 

 logically related, the history of the individual is a 

 very brief epitome of the history of the race. 



