68o 



THE RESPIRATION AND 



[PT. Ill 



is not regular, but has certain definite points of transition, and tends 

 to approximate rather to a series of straight Hues than to a segment 

 of a curve. The findings of Parnas & Krasinska, then, were in a sense 

 a return to the original interrupted curves of Bataillon. The respira- 

 tion of the amphibian embryo, said Parnas & Krasinska, during the 

 segmentation, morula, and blastula stages, is proportional to the 

 time passed and uniformly rising. The increase in the number of cells 

 is certainly accompanied by an increase in the respiration. But at 



250 



6a 



Hours 

 Fig. 131, ( Upper line = in air; lower line = in oxygen.) 



the time of gastrulation, there is a marked rise in the gaseous exchange 

 (see Fig. 132), and a further powerful acceleration of it is seen at 

 the time of the formation of the medullary plate, i.e. after the embryo 

 has formed its longitudinal axis. "The first cleavage processes", said 

 Parnas & Krasinska, "and the dividing of the embryo into poten- 

 tially different cells proceeds with a uniform amount of respiration, 

 but the differentiation of the germ-layers first of all, and then, the 

 formation of structurally and chemically different cells, are accom- 

 panied by enhanced metabolic intensity and therefore by an in- 

 creased respiration. After the neurula has been formed there is little 



i 



