DEVELOPMENT OF SPELERPES BILINEATUS 



177 



The relative numbers of the various sized granules are, however, 

 characteristic for a given zone. Fig. 2, b, c, d, e show the general 

 size relationships between the granules of the three zones. Very 

 large granules do not occur in the upper zone, nor do grooved 



o 



^ 







0. 







" d o 



a 



O 



0„ ° o 



o 



O 



c 



Fig. 2 



ones appear in the middle zone. Likewise, the smallest granules 

 do not appear in the lower zone. 



Contrary to Jordan ('93), Houssay ('90) and others who main- 

 tain that the size of the yolk granules are of no value for deter- 

 mining the future history of the various regions of the egg, I have 

 found that until after gastrulation at any rate, the differences 

 in size of the yolk granules afford a highly efficient means for 



