SPECIALIZATION OF CELLS. 1 53 



duction; and others, again, have formed themselves into 

 protecting organs for the little community, and so on. In 

 short, various classes or castes must have arisen in the 

 cell-state, following diverse occupations and yet working 

 together for the common end. In proportion as this 

 division of labour progressed, the many-celled organism, 

 or the specialized cell-community, became more perfect or 

 civilized. 



We may follow the comparison further. It may be 

 asserted a 'priori, that in consequence of the reciprocity of 

 relations which was occasioned by the struggle for existence 

 and the gathering of many organic individuals in a common 

 dwelling-place, when organic life first began on the earth, 

 a community of many similar individuals arose from a one- 

 celled organism ; that a division of labour afterwards took 

 place among these similar cells, and that finally, in conse- 

 quence of continuous specialization, a developed many- 

 celled organism with many different organs, all working 

 for a common. end, arose. In order fully to realize the value 

 of this significant comparison, it would be necessary to 

 enter in detail into the theory of the division of labour, or 

 specialization, which now plays a very important part in 

 Biology, especially since Darwin's Theory of Selection has 

 enabled us to understand the true causes of these phe- 

 nomena. At present I must refer for the more detailed 

 elaboration, which would carry us too far to be entered 

 into here, to Darwin's Doctrine of the Divergence of Cha- 

 racter, and to my lecture on the Division of Labour. We 

 shall hereafter return to this subject.^* 



At present we will rather examine whether the a priori 

 views on Phylogeny which we preconceived, are in accord- 



