CYLINDRICAL CYEMATA. 83 



larger, on the other hand, falls into this group. It may be recalled that a similar 

 instance of twins falling into different groups was mentioned in the discussion of 

 group 4, and two more instances will be mentioned in the succeeding group. 



The disproportion between the size of the cyemata and that of the chorionic 

 vesicle, though pronounced, is not so great in this as in the preceding group. What 

 was said there regarding the relation of the dimensions of the abortus to those of 

 the chorionic vesicle applies here also. As all the specimens of this group contain 

 cyemata varying from 2.5 to 13 mm., it is evident that the amnion must have 

 developed considerably in some of them. Subsequent retrogression of the cyema 

 or hydramnios, then, left the amnion proportionately too large as compared with 

 the cyema, for (so far as I am able to see) there is little retrogression in the 

 size of the amnion, even when that of the cyema is considerable or total. The 

 amnion generally was relatively too large, although rarely it was folded about the 

 cyema very intimately. When large it frequently was greatly folded, with adjacent 

 folds adherent to each other, and in one instance a small vesicle so constituted 

 could easily have been mistaken for a yolk-sac. The amnion in this case had under- 

 gone decided structural changes. 



The number of chorionic vesicles wholly encased in blood or in blood and 

 decidua was relatively small. The layer of blood which was interposed between 

 the decidua and chorion varied from 1 to 10 or more millimeters in thickness. 

 Whether the condition of this blood is of any value in determining the time that has 

 elapsed since the detachment of the conceptus and its expulsion from the uterus, 

 I am at present not able to say. The contrast between the states of preservation 

 of the blood and the contained conceptus naturally was sharp in many cases. 

 Often the blood was preserved well, even in instances in which the stroma of the 

 chorionic vesicle was very degenerate. The conceptuses in this group have pro- 

 gressed somewhat in development beyond those in the preceding group, both as to 

 external form and the internal organs, but in general the changes noted in the 

 cyema and its appendages, or in the chorion or amnion, or even in the decidua, 

 did not differ in kind from the changes noted in the previous groups. However, 

 since the specimens in this group are somewhat older, it would seem to follow that 

 the duration of these changes must have been somewhat longer. Nevertheless, 

 the rate of change must have been much slower. Hence a longer duration does not 

 necessarily imply the production of a more pronounced change. It is also not 

 impossible that, with increasing maturity, the tissues may become more capable 

 of resistance and thus affect the rate of change produced by a given cause of 

 constant intensity. 



As was true of some of the nodular cyemata, so also several of the cylindrical 

 were sessile, being attached directly to the amnion, sometimes by their caudal 

 extremities, apparently without the instrumentality of an umbilical cord. But, as a 

 rule, a short umbilical cord is present, even if not wholly normal in form, structure, 

 or relations. Indeed, the cord quite frequently is distended greatly, and micro- 

 scopic examination usually shows that the condition of the umbilical vessels, even 

 when present, is not normal. In many instances they are absent altogether and 



