434 MORGAN. [Vol. X. 



Further, the great disproportion in the later stages between 

 the whole amount of material in the germ-ring, and the amount 

 of material necessary to form the embryo, makes it quite 

 certain that during the late stages only a relatively small 

 amount passes into the embryo from the germ-ring. 



During the second period of overgrowth of the germ-ring 

 we have seen from surface preparations that the germ-ring gets 

 broader as it begins to close. Sections show us, however, that 

 this does not mean that it is quantitatively greater, but the 

 reverse. Everything points to the conclusion that during this 

 period, while the germ-ring is shrinking, it is also losing 

 cells to the extra-embryonic region. Its own cells become 

 flatter, and surface preparations produce the effect of lines of 

 cells running out from the germ-ring into the extra-embryonic 

 region. The latter effect may, however, be due to the shrink- 

 ing of the ring. The line of demarcation at this time between 

 germ-ring and extra-embryonic region is, in preparations, not at 

 all a sharp one, as the figures might seem to indicate, but we 

 find the germ-ring gradually fading out into the extra-embryonic 

 region. 



If it is admitted that the under layer of the germ-ring passes 

 continuously into the embryo, it follows with a good deal of 

 probability that the upper (second layer) does also. First, be- 

 cause of its close connection at the edge of the blastopore with 

 the under layer, and secondly, from the evidence furnished 

 by embryos whose development has been modified by artifi- 

 cial means. These embryos will be described in the next 

 section. 



Experimental. 



Removal of Blastomeres. 



In my preliminary paper published in the Anatomischer An- 

 zeiger, 1893, I have described the results of certain experiments 

 on the eggs of Fundulus. It was found possible to remove 

 from the ^gg one of the first two blastomeres without destroy- 

 ing the capacity of the remaining blastomere to develop. The 

 blastomere, at first flattened on one side where it had been in 



