3o8 



Charles Zeleny. 



The localization of morphogenic factors is not particularly 

 elucidated by the two larvae obtained. The one represented in 

 Figure loD has a solid interior cell mass, evidently an archen- 

 teric ingrowth. There is no other structure sufficiently differen- 

 tiated for our purpose. 



V. Elongated Egg to completion of first cleavage. The period 

 is limited on the one hand by the beginning of the lateral elonga- 

 tion of the egg and on the other by the completion of the first 

 cleavage. Five eggs were operated on. In every case the frag- 

 ments obtained show a partial cleavage from the start, even 

 though in several instances the cleavage furrow was slight at the 

 time of the operation, and there was still a broad connecting band 

 between the two parts of the egg. This band was in every case 

 equal to one-half or more of the diameter of a blastomere of the 

 two-cell stage. The two fragments from one of the eggs are 

 shown in Figures 1 1 A and B at the four-cell stage. It is evident 



Fig. II (x 216). 



Fragments from Eggs Bctzveni the Beginning of Lateral Elongation and the Coin- 

 pktion of the First Cleavage. 



A, four-cell stage of fragment {=111/2 of egg), obtained by a vertical cut. 

 Polar bodies are attached. The second furrow is equatorial. B, four-cell 

 stage from the other half of the same egg. 



that the cleavage is a partial one resembling closely that of iso- 

 lated blastomeres of the two-cell stage to be described later (p. 

 309) . One of the fragments has the two polar bodies still attach- 

 ed, and it is evident that the second cleavage furrow is equatorial 



