STUNTED CYEMATA. 89 



Whether or not twin cyemata fall into the same group of the pathologic 

 very evidently depends upon whether they have been subjected to identical 

 influences. That the exact conditions under which they develop may easily vary is 

 evident, and that they may be variously affected previous to implantation is also 

 possible. Nor does the occurrence of twins which fall into different groups neces- 

 sarily imply that the processes responsible for the physical differences were neces- 

 sarily or essentially different from those which are responsible for the disproportion 

 in size of normal, full-term twins. It may be simply a matter of degree. In the 

 case of 788 a, b, for example, the deciduse were infiltrated, but not to the same degree. 



A few of the specimens in this group are of particular interest because of the 

 great disproportion that exists between the size of the fetus and that of the chori- 

 onic vesicle. In No. 135, for example, in which the fetus was 9 mm. long, the 

 dimensions of the chorionic vesicle were 105 by 65 by 65 mm. Since the villi practi- 

 cally were absent and the surrounding layer of decidua was very thin, the above 

 dimensions practically are those of the amnion also, for it had fused with the 

 chorion. Although the wall of this abortus is composed of these three layers, it 

 nevertheless is almost papyraceous. Microscopic examination shows it to be 

 decidedly degenerate and to contain many leucocytes. The amnion, too, is very 

 degenerate, although its epithelium is still present. Even if mechanical distension 

 were the chief factor in the enlargement of this vesicle, it is unlikely that it was 

 solely responsible for the disproportion between the chorionic vesicle and the size 

 of the fetus. Part of this disproportion is attributable to some recession in the 

 size of the embryo, and more to the failure of the latter to develop normally. To 

 what extent the chorionic vesicle grew after the death of the fetus must remain 

 a matter of conjecture; but in view of its very degenerate character, it seems 

 unlikely that it could have grown much. The absence of the menstrual history 

 unfortunately leaves us without data that might be of some assistance in arriv- 

 ing at a conclusion regarding this matter. Although the organs of this fetus have 

 lost their clear definition, and although dissociation and maceration are marked, 

 yet on the whole it is preserved better than one would expect from an examination 

 of the chorionic vesicle. Though epidermal blebs are present, not all the epidermis 

 has sloughed. Indeed, in some places the superficial layer has formed marked 

 local thickenings which now and then are so definitely circumscribed that they 

 could probably be designated as warts or papilla?. Similar, although more diffuse, 

 epidermal thickenings are found also in No. 201, a fetus of 20 mm. The same phe- 

 nomenon apparently was observed by Rokitansky (1861), who spoke of papilla- 

 like growths of the epidermis in a fetus. 



The most interesting thing seen in the stroma of the villi of this group was the 

 presence of epithelial vesicles at various depths from the surface in No. 276. 

 Although many of these vesicles which are not well preserved could easily be con- 

 fused with degenerating vessels, in the case of others this is impossible, because 

 their relations to the epithelium can be established easily. The epithelial lining 

 of many of them is fairly well preserved, and in some instances the vesicles can 



