354 



EIOHARD ASSHETON. 



more loosely to that of the trophoblast. The fluid inside the 

 blastocyst would force the disc up into its place. 



^^^^-rr^/77m/7EMM/Mmi^Ip7r77/7. 



MHL 



TR- 



The changes of the blastodermic vesicle and its great in- 

 crease in lengtii, which occur during the twelve to fourteen 

 days, have been related by Yon Bacr, Coste, and BischofF, and 

 more recently, together with a detailed account of the changes 

 in the embryonal area, by Keibel. A brief account from me 

 will suffice in confirmation of their discoveries. 



From the moment of the rupture of the zona pellucida upon 

 the sixth day of development, there has been a constant ten- 

 dency for the vesicle to become elongated. By the twelfth 

 day it is 10 or 12 mm. long and only 3 mm. broad. It now 

 grows out with exceedingly great rapidity, and by tiie thir- 

 teenth or fourteenth day each embryo may measure as much 

 as a foot in length (30 cm.). 



The hypoblastic vesicle extends to nearly the same length 

 as the outer wall. Hence the whole blastocyst can be said to 

 be didermic. 



By the seventeenth and eighteenth days the vesicles have 

 attained to about their greatest length, and completely fill the 

 cavity of the two horns of the uterus. The length of each 



