THE VILLI IN ABORTUSES. 325 



of mesoderm into the trophodermic trabeculse. As soon as an area of the syncy- 

 tium and the Langhans layer becomes elevated at a given point, the mesoderm 

 accompanies them if this elevation represents a beginning villus. No matter how 

 marked the syncytial development, I have never noticed the presence of a normal 

 structure in the distal portion of a villus and a purely syncytial structure in the 

 basilar portion. No matter how long or how complicated the syncytial buds 

 became, they never were invaded by mesenchyme or became vascularized. How- 

 ever, this fact does not preclude the inclusion of blood within syncytial skeins or 

 trophoblastic nodules, or within invaginations of epithelium in the mesoderm of the 

 villi. All these appearances not infrequently are seen in specimens in which there 

 has been considerable growth of syncytium or of the Langhans layer, but I have 

 never seen evagination of these two layers without a mesodermal core. No matter 

 how long vascularization of a villus is delayed, and in some cases this seems never 

 to occur, such villi otherwise have the same structure as the rest, just as tropho- 

 blastic development on the early villi seems to be universal and not visibly influenced 

 in its first stages by the location of the embryonic disk or the shape of the early 

 conceptus. These facts undoubtedly are not without significance for the nutrition 

 of the early conceptus. The universal presence of villi establishes conditions much 

 more favorable to circulation of the surrounding fluids, besides very materially 

 increasing the area of absorption. Hence I do not believe that bare areas in the 

 basal and capsular regions of a young conceptus can be regarded as normal. 



Branching of the villi occurs exceedingly early and does not seem to develop 

 any special plan or be limited to any particular plane. The angle generally is an 

 acute one, probably because of the fact that the branches aim to reach the 

 trophoderm or the decidua. It is not at all uncommon to find several branches 

 arising at the same level, or they may leave the parent trunk in quick succession. 



Although considerable variation in size and complexity of the villi seems to 

 exist even in normal chorionic vesicles, these differences are not necessarily so 

 pronounced in the same as in different specimens. However, one not infrequently 

 meets with simple, unbranched villi among others of great complexity, but I did 

 not get the impression that, except in the first few months, much interpolation of 

 villi occurs later in development. It is quite surprising how large a placental 

 area can be formed by a single villous tree, and placental differentiation occasion- 

 ally seems to be present in chorionic vesicles with embryos of a length of only 

 17 mm., which implies an age of only about 7 weeks. Indeed, it does not seem 

 improbable to me that close observation will show that some placental diffentia- 

 tion exists as early as the sixth week. 



