2l6 CHAS. W. HARGITT. 



case in colonies which had been kept in the aquarium for a few 

 days. In these the pigmentation was appreciably less intense 

 than in specimens freshly collected. There were, however, not- 

 able exceptions in this respect among various specimens under 

 natural conditions. The same has been observed in Pennaria, 

 and is, indeed, a fact more or less well known in many animals. 

 Conklin ('05', p. 13) has cited similar cases among ascidians ob- 

 served by VanBeneden and Julin ; in some species two very dif- 

 ferently colored eggs being produced, one yellow, the other gray. 

 Both are said to develop normally and in the same manner, giv- 

 ing rise to larv?e whose entoderm cells are of the same respective 

 colors. 



In the case of C/ava there is no such distinction as this, though 

 the presence of more or less pigment has apparently no effect 

 upon the normal development of the embryo. In another point 

 there is also some measure of similarity, namely, in that as 

 development proceeds, the pigment which was at first distinc- 

 tively peripheral in position, seems later to become transferred 

 to the entoderm of the larva. This, however, as will be seen 

 later, is due not to any shifting of this matter from one region to 

 another, but simply its resorption by the more rapidly developing 

 ectoderm, while as yet the entoderm is only partially differ- 

 entiated. 



Whether this pigmentary zone formed a definite germinal area, 

 and its gradual development was an expression of the differen- 

 tiation of this area, or whether it might not be simply the results 

 of cytoplasmic metabolism associated with the formation of yolk 

 substance, or whether it might not, perhaps, be in some way asso- 

 ciated with the phenomena of maturation, seemed for a time some- 

 what uncertain. A study of the matter more critically in its 

 cytological aspects soon sufficed to discredit the last alternative, 

 namely, that it .was in any way associated with maturation. Fur- 

 thermore, the appearance of the pigment was too early in the 

 history of the egg to involve the operation of any maturation 

 phenomena. 



Again, several series of facts conspired to discredit the prob- 

 ability of the first alternative, namely, that it was in any sense a 

 differentiation of germinal substance. Of these the following may 



