THE ORIGIN OF CHORDATES 
BY | 
Dr. H. C. DELSMAN 
(Continued) 
IL 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 1 found that the views l 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, Il have of course eagerly cited them. 
And since to my delight 1 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. 1 must therefore emphasize that the greater part 
of the numerous quotations have been gathered from the 
literature only after l 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. 
