180 W. B. CHAPMAN 



heart itself was removed, and the changes in its blood-vessels 

 were similar. 



The chicks were incubated varying lengths of time from 

 twenty-four hours up to and including ten days after the opera- 

 tion. I was unable to keep any of the chicks alive longer than 

 nine days, that is, about eight days after the operation. The 

 mortality for chicks up to the end of the ninth day of incubation 

 was about fifty per cent. After the egg has been incubated as long 

 as desired, it is again opened and the vessels injected with India 

 ink. The specimen is fixed in Bouin's solution, which may be 

 applied to the chick while on the egg, or, preferably, after the 

 embryo has been removed and flattened out on a slide. The 

 specimens are stained faintly and cleared in oil of wintergreen 

 (Spalteholz method), or, if desired, mounted permanently in 

 damar. After being studied, the embryo has, in some cases, 

 been embedded and sectioned. 



Before injecting, a careful search is always made for remnants 

 of the heart or any pulsating blisters, such as I will describe a 

 little further on in this paper. 



IV. DESCRIPTION OF THE EXTRA-EMBRYONIC VASCULAR SYSTEiM 

 OF EMBRYOS STUDIED 



The appearance of the embryo at the stage of operation is 

 shown fairly well in figure 1, which represents an embryo slightly 

 beyond the operative stage At this period the blood cells have 

 not acquired their hemoglobin and no vessels are visible under 

 the binocular. The embryo appears to be floating free within 

 the clear area pellucida, and the area opaca is apparent only as 

 a wide milky-white band around the area pellucida. The blood 

 vessels in the embryo proper of chicks of this age have been 

 studied by Miss Sabin (T7) through injectiods of India ink into 

 the aorta and larger vessels, and her results have already been 

 referred to. 



As previously mentioned, and as shown in figure 1, the vessels 

 of the extra-embryonic region consist of a dense capillary net 

 extending from the embryo to the sinus terminalis at the time 

 the circulation begins. Anteriorly, the sinus terminalis breaks 



