So T. H. MORGAN. 



bUstoccel had reached its highest point of development, and the 

 other at the time when the dorsal lip of the blastopore had just 

 appeared on the surface. Sections showed that the blastoccel was 

 emptied in large part, yet in both cases gastrulation took place. 

 There is, however, to be noticed a distinct retardation in the lime 

 of gastrulating between the normal and the injured eggs. The 

 hole made in the roof closes almost at once, but a lump of cells 

 generally indicates, throughout the gastrulation process, the place 

 of injury. Owing to the closure of the top, the pressure rela- 

 tions of the cells will be again largely reestablished, but the 

 delay in the time of gastrulation indicates that the injury has to 

 some extent interfered with the processes involved in the act of 

 gastrulating. 



The results show that Rhumbler's hypothesis is probably in- 

 correct at least so far as the blastoccel is concerned. If however 

 he should shift his position and assume that it is the accumula- 

 tion of waste substances in the interior of the egg itself, /. e., in the 

 middle of the yolk-cells, that causes the invagination, the results 

 are not fatal to his view. I attempted therefore to test Rhumbler's 

 hypothesis in another way. If the amount of carbon dioxide 

 outside the egg can be made equal to that in the interior, the proc- 

 ess of gastrulation should not occur, if Rhumbler's view is cor- 

 rect. I placed frog's eggs in the late blastula stages in a bottle 

 containing some water. By means of a tube running beneath 

 the water I forced air that I had held in my lungs for a few sec- 

 onds through this water. The air above the water was also dis- 

 placed through an outlet. The communications with the out- 

 side were then closed. It seemed probable that there would be 

 as much, and probably a great deal more carbon dioxide out- 

 side the eggs than inside, yet during the following six to twelve 

 hours the gastrulation took place in the normal manner. This 

 result also is not favorable to Rhumbler's interpretation. Other 

 observations and experiments have led me to think that the proc- 

 ess of gastrulation cannot be explained by such mechanical proc- 

 esses as surface tension, and I have tried to show elsewhere l 

 that the change in shape of the cells that leads to the invagina- 

 tion is due to a process of active contraction of the cells, which 



r'.f .-/;-<-// /z-, XIX., 1905. 



