RELATION OF CYEMIC TO CHORIONIC SIZE. 173 



Evans, in an undated circular issued by this laboratory, gave the length of 

 the embryo and the size of the chorionic vesicle as indicated in table 5. Such 

 tabulations as these are very helpful and suggestive and are bound to gain much 

 in value with enlargement of the data upon which they are based. This table from 

 Evans indicates that the conceptus of the third week practically is spherical, that 

 it then rapidly becomes oblong so that its greatest diameter is almost twice that 

 of the second dimension by the fourth week, and that it returns to a more spherical 

 condition in the sixth, seventh, and eighth weeks, during which time its greatest 

 dimension is indicated as only one-sixth longer than the second dimension. Upon 

 comparing the length of the cyema with that of the conceptus as given in table 5, 

 we find that the greatest dimension of the latter is 10 times that of the former in 

 the third week. The greatest dimension of the chorionic vesicle is approximately 

 6 times that of the embryo in the fourth week; 4.5 times in the fifth week; 3 times 

 in the sixth week; 2.2 times in the seventh; and 1.4 times in the eighth. From 

 this it is seen that there is a rapid and early approximation between the greatest 

 dimension of the chorionic vesicle and the length of the cyema. This might be 

 expected from the fact that growth in length of the cyema is so much greater than 

 growth in the other two dimensions. The irregularities evident in this table 

 probably are attributable to the small series available for the tabulation, to the 

 fact that all measurements of necessity had to be made postpartum, and that they 

 were not made by the same individual. 



The exact form of the human conceptus in its early stages still remains un- 

 known, but as indicated by specimens from the literature, it is probably spherical. 

 This sphericity, however, must be lost as soon as the conceptus extends across the 

 uterine cavity or when the cyema reaches a length which brings its cephalic and 

 caudal extremities closer to the chorionic membrane than are the rest of its sur- 

 faces. From this time on we might expect the form of the conceptus to become 

 more and more elongated and ovoid. It may be recalled that one of Leopold's speci- 

 mens of early conceptuses was represented as ovoid or as almost cylindrical even, 

 but one must bear the possibility of molding during abortion and of postpartum 

 distortion in mind. However, it often is difficult to detect elongation attributable 

 to molding during labor, even in conceptuses of considerable size. Conceptuses 

 up to 4 and 5 cm. in greatest dimension usually assume a flattened, ovoid form 

 when placed in fluid of approximately the same specific gravity. One might, I 

 presume, suppose that after the first weeks all conceptuses have a more or less 

 cylindrical form, in consequence of the shape of the uterine or tubal cavities, but 

 the form of early guinea-pig conceptuses throws doubt upon this supposition. 

 They are quite spherical, and the same thing is true of young rabbit conceptuses, 

 even when they have considerably distended the thin-walled cylindrical uterine 

 cornua by reaching a size of one centimeter. 



What is needed, however, is a careful series of measurements on selected 

 material, although even such material will not be ideal as long as we remain unable 

 to differentiate early normal from abnormal forms and as long as not all measure- 

 ments are made either on fresh or on fixed material. Hence it is evident that the 



