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STUDIES IN GENERAL PHYSIOLOGY 



may begin to segment somewhat later than the rest of the 

 egg. The influence of the quantity of the egg-substance 

 upon the formation of the gastrula is, however, an unques- 

 tionable one. The substance which remained within the egg 

 has developed in Fig, 77, twenty-four hours after fertiliza- 

 tion, to the gastrula stage. According to Fig. 75 ? its mass 

 is about twice as great as that of each of the two blastulse 

 which arose from the extraovate, and which at this time had 



FIG. 79 



FIG. 81 



FIG. 82 



FIG. 83 



not yet reached the gastrula stage. I have observed this 

 over and over again; as, for example, in Fig. 78, where the 

 small extraovate b has formed a blastula, while the rest of 

 the egg a has formed a gastrula. The cultures kept in a 

 drop of water always died in the course of the second or 

 third day. The large pieces reached the pluteus stage dur- 

 ing this time, while the smaller pieces remained in the blas- 

 tula or gastrula stage. In order to follow the further fate of 

 these small fragments of the egg after the second or third 

 day, I had to rely on the material from the cultures kept in 

 the larger dishes. Figs. 79-83 represent the relation between 

 mass and development in a culture two days old. Fig. 73 

 shows the size of a fertilized but undeveloped egg of this 

 culture two days old ; Fig. 79, the size of a pluteus that had 

 developed from an entire egg, which, however, had been 



