The developmect of the urinogenital organs of the lamprey. 77 



brates would seem to account for the difference in the stages in which 

 we are able to recognize the earliest indications of sex-cells in the 

 ontogeny. It may be added that this conservatism in the sex-cells 

 is not only apparent in such superficial characters as size and pro- 

 longed retention of yolk, but also in the structure of the nucleus, 

 e. g. the retention of four chromatin loops of the primitive form in 

 the sex-cells of the embryo Ascaris. 



The Hull Zoological Laboratory, 

 University of Chicago, March 20 th, 1899. 



