CHAPTER II A . 



STRUCTURE.* 



54a. As, in the course of evolution, we rise from the 

 smallest to the largest aggregates by a process of integration, 

 so do we rise by a process of differentiation from the simplest 

 to the most complex aggregates. The initial types of life are 

 at once extremely small and almost structureless. Passing 

 over those which swarm in the air, the water, and the soil, 

 and are now some of them found to be causes of diseases, we 

 may set out with those ordinarily called Protozoa and Pro- 

 topliyta: the lowest of which, however, are either at once 

 plants and animals, or are now one and now the other. 



That the first living things were minute portions of simple 

 protoplasm is implied by the general theory of Evolution; 

 but we have no evidence that such portions exist now. Even 

 admitting that there are protoplasts (using this word to in- 

 clude plant and animal types) which are without nuclei, still 

 they are not homogeneous they are granular. Whether a 

 nucleus is always present is a question still undecided; but 

 in any case the types from which it is absent are extremely 

 exceptional. Thus the most general structural traits of pro- 

 toplasts are the possession of an internal part, morpho- 



* When, in 1863, the preceding chapter was written, it had not occurred 

 to me that there needed an accompanying chapter treating of Structure. 

 The gap left by that oversight I now fill up. In doing this there have been 

 included certain statements which are tacitly presupposed in the last chap- 

 ter, and there may also be some which overlap statemen! s in the next chapter. 

 I have not thought it needful so to alter adjacent chapters as to remove these 

 slight defects : the duplicated ideas will bear re-emphasizing. 



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