Reptile compared with Mammal and Bird 



49 



But in the Eeptile at this stage there has been very little 

 accumulation and therefore presumably very little tension. 



The accumulation of fluid does occur later, but not until the 

 deuterogenetic centre has become well established, and the result 



bl 



Fig. 27 after Brauer, 1907. Longitudinal section 



through the egg of Hypogeophis. 

 bl blastopore; ec ectoderm; en endoderm; gc future gut cavity. 



is therefore a mass of cells in the form of a heap instead of a long 

 drawn out streak, as in the case of Mammals and Birds. 



When the accumulation does come, that is to say when the 

 stretching is produced which results in the rupture of the posterior 



Fig. 28. A, Mammal; B, Bird. 



Diagram to compare corresponding stages in the formation of the segmentation 

 cavity, be blastocyst cavity; sg segmentation cavity. 



part of the roof of the subgerminal cavity or archenteron, there 

 occurs at the same time a perforation within the deuterogenetic 

 tissue which corresponds in position with the metenteric opening 

 referred to in a previous paragraph. 



