RELATION OF CYEMIC TO CHORIONIC SIZE. 175 



Since the number of conceptuses with embryos of the first month which have 

 been measured is exceedingly small, any curve based on these data necessarily 

 must remain largely conjectural. However, if we regard it as purely tentative, 

 even such a curve nevertheless may be of value. Moreover, its obvious incom- 

 pleteness will prompt to improvement. As will appear from Chart 1, only 16 cases 

 were available for the construction of the curve for the first month ; 8 of these were 

 from our own collection, 8 from the literature. One of the two embryos, 2.5 mm. 

 long, belongs to a vesicle which is entirely too large and hence falls high on the 

 chart. On consulting the history of the case it was learned that the conceptus was 

 decidedly collapsed and hence very probably distorted. But this is not the only 

 specimen which shows considerable disproportion between the size of the cyema 

 and the conceptus. I do not imply, however, that these disproportions represent 

 wholly normal variations, although until a large series is available for study it will 

 remain impossible to determine the deviation from the average of normal speci- 

 mens in a given state of development. 



The field represented in Chart 1 was plotted from measurements of chorionic 

 vesicles and cyemata below the fourth month, which are listed as normal in the 

 Carnegie Collection. It includes both uterine and tubal specimens; the former 

 are represented by dots and the latter by circles. In addition to these specimens 

 the measurements of 12 young conceptuses from the literature have also been 

 added ; these are represented by crosses. Since scrutiny of the fields made by the 

 use of other than only the greatest dimension of the chorionic vesicle made it 

 evident that the other dimensions were quite useless as criteria, only the greatest 

 measurement was used for the construction of the field as here represented. The 

 greatest dimension of both cyema and chorionic vesicle is represented in milli- 

 meters the former on the ordinate and the latter on the abscissa. 



Reference to the location on the field of the cases from the literature, and 

 also an inspection of the beginning of the curve, show that the chorionic vesicle 

 forges ahead of the cyema in its growth. This is what one would expect, for 

 embryonic differentiation naturally must be delayed at the start. However, the 

 specimens of conceptuses with a measurement of less than 10 mm. are too few to 

 enable one to regard this part of the curve as more than an approximation of the 

 actual. Between a length of 10 and 20 mm. a considerably larger number of cases 

 are found, and here the curve is more reliable, although considerable scattering 

 of the cases nevertheless is present. To what extent this scattering is due to 

 variations to growth, and to what degree to the fact that the material was perhaps 

 not strictly fresh or normal, it is impossible to say; probably both factors are 

 involved. Moreover, since the chorionic measurements were external, the con- 

 dition and length of the villi introduce a further factor of fluctuation; for although 

 the average dimensions of normal villi may fluctuate very little in length when 

 large series of conceptuses are concerned, they do vary considerably, not only in 

 different but also in the same specimen. This is especially true when the period 

 of placental differentiation is reached. Hence measurements of the cavity of the 

 chorionic vesicle or those taken from the wall of the bisected vesicle would give 





