PATHOLOGIC OVA, ALBINO RAT 139 



adjustment was found necessary, none of the right wall of the 

 larger egg-cylinder, and only very slightly so of its left wall. 

 The slight deviation from the longitudinal axis of the larger egg- 

 cylinder made the procedure desirable. It is thought that the 

 figure as presented gives correctly the size of the respective egg- 

 cylinders, and in all essentials, their relations; the greater part 

 of the figure having been drawn from one section. Both of the 

 egg-cylinders reveal normal structure for the stages of develop- 

 ment attained. The larger one is cut in the coronal plane, as is 

 readily determined by the distribution of the mesoderm, one side 

 representing a mirror picture of the other. The direction of sec- 

 tion in the smaller egg-cylinder, except that it is longitudinal, 

 is not to be determined, since before the anlage of the mesoderm, 

 a bilateral symmetry cannot be recognized in sections. Since 

 these two egg-cylinders are in all essentials of normal form and 

 structure, and since their structure is clearly brought out in the 

 figure, an extended description of them at this place seems un- 

 called for. For respective stages the reader is referred to Part I. 

 Attention may be drawn, however, to the fact that the visceral 

 entoderm on the contiguous surfaces of the two egg-cylinders is 

 less fully differentiated, and shows less absorption of the ma- 

 ternal hemoglobin than is seen on the exposed or free surfaces, 

 this, no doubt, for mechanical reasons. Further, that in the 

 region where the two egg-cylinders are in contact, the parietal 

 ectoderm of each can be traced as a distinct layer to the bases 

 of the respective ectoplacental cones, showing that each developed 

 from a separate ovum. The ectoplacental cones are for a short 

 distance distinct. In tracing the sections through the series the 

 impression is gained that the ectoplacental cone of one of the egg- 

 cylinders overlaps that of the other in such a way that in the 

 plane of the sections obtained, one seems continuous with the 

 other, as represented in the figure. The boundary between the 

 two is not distinct, and it would seem that as a result of pres- 

 sure, partial fusion of the two had taken place. The presence 

 of two egg-cylinders, enclosed within a single decidual crypt, as 

 shown in this figure, with one of them having much smaller size 

 and representing a younger stage of development, I believe is 



