846 EIOHARD ASSHETON. 



The Rupture of the Rauber Layer. The Tenth and 

 Eleventh Days. 



I have now reached the stage of which we have recently had 

 a description from Weysse (24). In this paper Weysse 

 described a very remarkable overgrowth, which, starting from 

 tlie edges which he assumed to be the posterior and lateral 

 margin, grew forwards over the embryonal area. 



According to his description both the embryonic epiblast 

 and the trophoblast cells were concerned in this process. 



It must be remembered, however, that Weysse did not 

 regard this as the real trophoblast, but as the definite extra- 

 embryoual area epiblast. He thought that he had evidence of 

 a third layer, the true Rauber layer, outside this again. On 

 this I shall have some more remarks to make. 



The overgrowth, according to him, formed a complete cover- 

 ing, or, as he termed it, a bridge, over the hinder part of the 

 embryonic epiblast. Ultimately the bridge was said to fuse 

 with the underlying embryonic epiblast, and to give rise to the 

 embryonic area. 



Weysse compares this overgrowth to the apparent growth 

 of the epiblast over the neural plate from the hinder part of 

 tiie embryo of Amphioxus. To this conclusion he seems to 

 have been brought chiefly by finding in certain sections a very 

 narrow canal leading from the exterior under his bridge into 

 the space between the epiblast and the livpoblast, or rather into 

 the space between the epiblast and a non-cellular membrane, 

 wiiich is apparently the homologue of that which Schafer (24) 

 found in the cat, and called the membrana limitans hypo- 

 blastica. This canal Weysse considered to be equivalent to 

 the neurenteric canal. The important difference that the sup- 

 posed canal leads into the space noticed above, and not into 

 the archenteron, does not seem to have influenced his opinion. 

 Duval (13) and Hubrecht (17) both comment on Weysse's 

 discovery, and each interprets the facts differently. 



