188 



W. B. CHAPMAN 



formed in the extra-embryonic region after the time when the 

 circulation should begin, and with its disappearance and the 

 breaking-up of the sinus terminalis into capillaries, which will 

 be described in detail below, the condition becomes uniform 

 throughout the extra-embryonic region. 



Fig. 5 A camera lucida drawing of tho anterior vitelline vein in an operated 

 chick of 60 honrs incubation (30 hours after operation). 



Fig. 6 Camera lucida drawini^ of the anterior vitelline vein in an operated 

 chick of 63 hours incubation (30 hours after operation). 



Fig. 7 A camera lucida drawing of the anterior vitelline vein in an operated 

 chick of 80 hours incubation (48 hours after operation). The vessel has grown 

 much narrower and is beginning to break up into capillaries nearer the embryo. 



