CiH 



CHAPTER III. 



Gastrulation and earliest development. 



As the reader will have observed, the conclusions reached 

 in the foregoing chapter are based for the greater part, not 

 on investigations of the writer himself, who until now has 

 worked more on Invertebrate than on Vertebrate develop- 

 ment, but on researches made by numerous other anatomists 

 and embryologists. Whenever i found that the views 1 was 

 led to had been pronounced in some form or other by 

 those who have worked on the subject themselves, inde- 

 pendently from the theoretical considerations on which my 

 conclusions were based, I have of course eagerly cited them. 

 And since to my delight I found this to be often the case, 

 the reader will perhaps have got the impression that my 

 theory is for a great deal nothing but an anthology and 

 compilation of thoughts more or less distinctly pronounced 

 by others. I must therefore emphasize that the greater part 

 of the numerous quotations have been gathered from the 

 literature only after I had worked out the theory, though 

 sometimes they have also indicated to me the direction in 

 which to continue. In this last chapter, where the earliest 

 stages of development will be dealt with, I now can give 

 also a few of my own observations which, 1 believe, con- 

 tribute a good deal to consolidate the foundations on which 

 my theory rests. 



