656 H. CALDWELL. 



Ovum. — The ovum arrives in the uterus from the Fallopian 

 tube at a very early stage. In one instance I found an unseg- 

 mented ovum in the uterus. 



Uterus. — Both uteri are very much enlarged in the early 

 stages, and up to the time when the blastodermic vesicle 

 measures about 8 mm. in diameter, the unoccupied is equal in 

 size to the occupied uterus. The size of the uterus during 

 gestation is due to the enormous development of its inner 

 lining. The muscular coat also becomes slightly thicker. 

 This inner lining is composed of a number of coiled tubular 

 glands. Each gland is a hollow tube with large secreting cells 

 forming the wall. Each gland opens separately by a small 

 pore into the cavity of the uterus. I believe that the function 

 of these glands is to supply a nutritive fluid for the growth of 

 the young embryo. There is no vascular connection 

 developed in any stages of the development between 

 the embryo and the uterine wall. 



The blastodermic vesicle lies quite unattached in the uterus. 

 The zona radiata persists until the vesicle attains a diameter 

 of 15 mm. 



Subzonal membrane. — Meanwhile the amnion forms in 

 the ordinary way. The false amnion continuous with the 

 ectoderm covering the blastodermic vesicle I shall speak of as 

 subzonal membrane. 



While the embryo is being folded off from the yolk-sac 

 another process is going on at the same time. 



Yolk-sac. — The yolk-sac grows round the embryo in the 

 sam emanner that the amniotic folds did in an earlier stage. 

 This may be also described by saying that the embryo sinks 

 into an indentation in the side of the yolk-sac, which finally 

 forms an almost complete investment similiar to the amnion 

 and closely overlying that membrane. The walls of these yolk- 

 sac folds, however, do not meet. They leave a circular area 

 where the amnion is only separated by fluid from the subzonal 

 membrane. 



Allantois. — Into this circular area the allantois grows, and 

 in the last period of intra-uterine life completely fills up the 



