8 INTRODUCTION. 



development of this ' nuclear zone ' in the eggs of the cod escaped my 

 observation when I studied the development of that species in 1881, 

 but I have during the past year (1885) observed it, and have moreover 

 satisfied myself that it arises as observed in Ctenolabrus, by Agassiz and 

 Whitman." 



The testimony of a number of other writers to be noticed in the 

 course of this work goes to show that the development of the periblast 

 on the other side of the Atlantic is not very different from what we 

 have noted on this side, and so there is reason to hope that the facts 

 presented in this paper will place this question beyond the necessity, if 

 not beyond the reach, of further controversy. 



