158 T. THOMSON FLYNN 



pressure of the gland secretion, evidenced by the swelling of 

 the gland and the formation of lateral fissures in the Plas- 

 modium. Such appearances are characteristic of all the glands 

 in this stage. 



When such glands are sectioned obliquely or transversely 

 they appear in sections of the diploplasma as irregular spaces 

 without any definite epithelial bounding layer. 



Attachment of Allantois. — At this stage this has 

 occurred over an approximate area of 0-5 by 0-21 mm. The 

 attachment is due to an intimate fusion of the splanchnic 

 mesoderm of the allantois with the somatic mesoderm of the 

 chorion. Apparently the allantois spreads its area of attach- 

 ment very rapidly, and one of its almost immediate results is 

 a quickening of the proliferating activity of the cytoblast cells. 



In the centre of the area of attachment the distinction 

 between the plasmodial layer and the cytoblast to a great 

 extent breaks down, the cell outlines of the latter disappearing 

 and its nuclei being converted into plasmodiblast nuclei. It is 

 in these positions that apparently the union of the allantois 

 with the chorion is best effected. This dissolution of the 

 cytoblast allows maternal capillaries to come closer to the 

 surface of the diploplasma, and this can be seen in some cases 

 even before the allanto-chorionic fusion is in being (fig. 14). 



Stage 3 , P e r a m e 1 e s o b e s u 1 a , 7mm. 



This is Hill's Stage C, being his earliest placental stage. It 

 is represented in the Department of Zoology of the University 

 of Sydney by a single slide containing one section. The 

 specimen, however, is well stained and mounted, and shows 

 all the details of the relations of the foetal membranes to the 

 uterine wall. 



The excellent general account given by Hill of the foetal 

 membranes of this stage renders any further description un- 

 necessary. I will therefore confine myself to a consideration 

 of the maternal and foetal structures associated with the 

 allantoic placentation. 



The attachment of the allantois may now be said to be com- 



