DEVELOPMENT OF THE PIG DURING FIRST TEN DAYS. 343 



The degree to which the embryos become crumpled is rather 

 interesting. No doubt the rupture of the zona radiata very 

 greatly affects the osmotic properties of the walls as a whole. 

 Up to this time it would seem that the accumulation of the 

 fluid within the cavity of the blastodermic vesicle was in excess 

 of the growth of the cell walls^ and so caused a great tension 

 to be placed upon them. Now it seems that the accumulation 

 is unable to keep pace with the growth of the walls, and con- 

 sequently the crumpling which they undergo is quite extra- 

 ordinary. It reaches its maximum about the middle of the 

 ninth day, after which the fluid gains upon the excess of wall 

 growth, and so the vesicle becomes again distended, and by 

 the eleventh day the creases have to a large extent become 

 smoothed out. 



During the eighth and ninth days a fluid is poured out into 

 the cavity of the uterus from the cells lining the cavity of the 

 uterus and the glands, which contains many corpuscles, which 

 may often be found adhering to the walls of the vesicles. 

 These corpuscles are clear and colourless, and do not readily 

 take stains. The amount of this fluid is, however, slight in 

 comparison to that poured out into the cavity of the sheep's 

 uterus. 



Eighth and Ninth Days— Stage D. 



The changes that occur during the eighth and ninth days 

 are not very remarkable. They are chiefly visible in the large 

 increase in size of the whole blastodermic vesicle, in the 

 spreading of the hypoblast layer, and consolidation of the 

 epiblast. 



The hypoblast at the moment of its first separation from 

 the inner mass forms a kind of network, which lines at first 

 the embryonic pole only of the blastocyst (fig. 21, H.) . During 

 the eighth and ninth days it extends its borders, and before 

 the end of the eleventh day it practically lines the entire 

 blastocyst. At this time the part lining the lower pole of the 

 blastocyst is still a network^ while at the embryonic pole it is 



