I04 Darwin^ and after Darwin, 



condensation, but also in the way of excision. Many 

 pages of ancestral history may be recapitulated in 

 the paragraphs of embryonic development, while 

 others may not be so much as mentioned. And that 

 this is the true explanation of what embryologists 

 term " direct " development — or of a more or less 

 sudden leap from one phase to another, without any 

 appearance of intermediate phases — is proved by the 

 fact that in some cases both direct and indirect develop- 

 ment occur within the same group of organisms, some 

 genera or families having dropped out the intermediate 

 phases which other genera or families retain. 



The argument from embryology must be taken to 

 begin with the first beginning of individual life in the 

 ovum. And, in order to understand the bearings of 

 the argument in this its first stage, we must consider 

 the phenomena of reproduction in the simplest form 

 which these phenomena are known to present. 



The whole of the animal kingdom is divided into 

 two great groups, which are called the Protozoa and 

 the Metazoa. Similarly, the whole of the vegetable 

 kingdom is divided into the Protophyta and the Meta- 

 phyta. The characteristic feature of all the Protozoa 

 and Protophyta is that the organism consists of a 

 single physiological cell, while the characteristic of all 

 the Metazoa and Metaphyta is that the organism 

 consists of a plurality of physiological cells, variously 

 modified to subserve different functions in the 

 economy of the animal or plant, as the case may be. 

 For the sake of brevity, I shall hereafter deal only 

 with the case of animals (Protozoa and Metazoa); but 

 it may throughout be understood that everything 



