132 G. CARL HUBER 



cant that in the two rats in which the pathologic condition affects 

 primarily the maternal tissue, the uterine mucosa, all of the con- 

 tained ova are prone to degeneration. In the abnormal ova 

 previously described, for which it was suggested that the causes 

 for the abnormality were to be sought in the ova themselves, 

 in the great majority of instances, only one abnormal ovum was 

 found in each uterus along with a variable number of ova which 

 are to be regarded as normal for the respective stage. 



IMPERFECT DEVELOPMENT OF THE ECTODERMAL VESICLE 



The series contains two ova, very favorably cut, ova in which 

 the ectodermal vesicle with the antimesometrial portion of the 

 proamniotic cavity does not seem to have developed normally. 

 Stages showing the differentiation of the egg-cylinder, the for- 

 mation of the ectodermal vesicle with the antimesometrial por- 

 tion of the proamniotic cavity, the formation of the mesometrial 

 portion of the proamniotic cavity in the extraembryonic ecto- 

 derm, the union of the two primary proamniotic cavities to form 

 a single space, are clearly shown in figures 26 and 27, Part I, in 

 the series of closely approximated stages there port rayed. From a 

 study of these figures, it will be observed that the antimesometrial 

 portion of the proamniotic cavity develops within the ectodermal 

 node before the mesometrial portion of this cavity develops in 

 the extraembryonic ectodermal portion of the egg-cylinder. In 

 the egg-cylinder shown in figure 8, rat No. 94, 8 days after the 

 beginning of insemination, such is not the case. In the uterus 

 of this rat there were found seven egg-cylinders, one of which, 

 very favorably cut, is shown in C, figure 27, Part I. The other 

 egg-cylinders obtained from this uterus, except the abnormally 

 developed one to be discussed, though not favorably cut, present 

 essentially the same form and structure as that figured under C 

 of the figure above referred to. The egg-cylinder portrayed in 

 figure 8 compares in size and form with those regarded as normal 

 and taken from the same uterus. For the greater part it presents 

 normal structure and normal relations of cells. The ectopla- 

 cental cone, only in part included in the figure, and the parietal 



