54 P^KANLKIN P. MALL 



Imt tho cliango in it is so complete that it is difficult to recognize 

 the diffei'cnt ])arts of the embryo except in a general way (fig. 4). 

 The coelom, heart and central nervous system can readily be 

 made out. Sometimes there are pigmented spots in one or two 

 of the sections, marking the position of the eyes. This group 

 again divides into two quite sharply circumscribed sub-groups: 

 first, those with an umbilical cord to which the dissociated 

 embryo is attached together ^vith the umbihcal vesicle; and 

 second, a vesicular group composed of specimens in which there 

 is only the remnant of the umbilical vesicle, the embryo being 

 nearly or entirely destroyed. Had it been possible in every 

 instance to differentiate between these two types of specimens 

 in the primary examination, they would, of course, have been 

 recorded as separate groups; but this could not be done without 

 sections and a microscopic examination. Therefore, for the 

 present we must consider them together. In our ordinary 

 laboratory parlance we speak of them as the nodular group. 



In the third group, both embryo and umbilical vesicle are 

 completely destroyed, but we can see within the degenerated 

 chorionic sac a more or less complete amnion. This group is 

 designated as the one in which the specimens are composed only 

 of the chorion and the amnion (fig. 3). 



In the second group the amnion is destroyed and there re- 

 mains only the chorionic vesicle containing the coelom. This 

 is usually filled with reticular magma and scattered cells, which 

 may represent all that is left of the embryo (fig. 2). 



Finally in the first group the form of the ovum is destroyed 

 and the specimen consists only of the \dlli which have under- 

 gone fibrous or mucoid degeneration. Sometimes only a few 

 of the \dlli are found, at other times there is a large cluster cling- 

 ing to a single stem, and some specimens are composed of large 

 masses of villi which form malignant hydatidiform moles. Such 

 a mass may weigh a kilogram (fig. 1). 



It can be readily seen that the above classification into sub- 

 groups is arranged somewhat in the order of the age of the ovum 

 when it began to degenerate. Generally these changes are so 

 pronounced that the embryo cannot live through the duration 

 of pregnancy and this accounts for the abortion. 



