APP.] BLASTODERMIC VESICLE. 465 



XIII. Ezamiuation of the blastodermic vesicle, 72 — 90 hours. 



A. To obtain the embryo see XII. D. 



B. Prepare the ovum either as in XII. B. or D. 



or in picric acid see I. B. i. 



C. Surface view, or in section see I. B. 3. 

 Observe : — 



1. The great increase in size of the ovum and the 

 reduction in the thickness of the membranes. 



2. The flattened layer of outer cells enclosing a cavity. 



3. The rounded cells of the inner mass attached as a 



lens-shaped mass to one side of the vesicle. 



XIV. Examination of a blastodermic vesicle of 7 days, 

 in which the embryonic area and primitive streak are 

 present. 



A. To obtain the embryo. 



On opening the body cavity the uterus will be 

 found to be uniformly svrollen and very vascular. 



Remove the uterus and open it carefully veith 

 fine scissors along the free, non-mesometric edge, 

 taking care to keep the point of the scissors -within 

 the uterus close against its wall. 



Observe 



1. The oval thin-walled vesicles lying at intervals 

 on the walls of the uterus. 



2. The presence of the pyriform embryonic area, at 

 the posterior end of which is seen the primitive 

 streak. 



f. & B. 30 



