Lt 



FIG. I. A diagrammatic representation of an approximately dorsal view of a 

 chorionic vesicle taken from the uterus about two weeks (estimated) before the young 

 would have been born. Three of the ovoid areas are in view, and the broken lines 

 represent the lines along which the amniotic partitions meet the inside wall of the 

 chorion. The clear areas at the ends are broken into by the scallops of the ovoid 

 areas. In this, as in the succeeding figure, the points of attachment of the umbilical 

 cords are indicated by large dots. Note especially that the indentations between the 

 scallops of areas 3 and 4 are much shallower than those between areas 2 and 3, 

 leaving a broader connection between the former than between the latter. This is an 

 indication that embryos 3 and 4, located respectively on dorsal and left lateral areas 

 (similarly embryos I and 2, located on the ventral and right lateral areas), are natural 

 pairs. For the significance of this arrangement see table and text. One half natural 

 size. 



FIG. 2. A view of the distal end of the preceding figure. This is introduced to 

 show the relation existing between the amniotic partitions within the chorionic cavity. 

 The figure also brings out the fact that the embryos may be paired, together with the 

 ovoid areas to which they are attached by the umbilical cords. One half natural size. 



FIG. 3. This shows a chorionic vesicle in situ, as revealed by splitting open the 

 uterus along the mid-ventral line. The age of this vesicle is estimated at one month. 

 Unfortunately the splitting was done before the specimen reached our hands, and ex- 

 tended so deep as to divide the vesicle into two parts. The parts, however, were 

 well preserved in sitzt, and the reconstruction could be made with certainty. Note 

 that the vesicle is octaedronal in shape, and that its entire surface is covered with 

 villi. Natural size. 



