402 JAS. p. HILL. 



the deeper lobular zoue of the syncytium, while scattered 

 nuclei also occur in its superficial portion just as in Stage B 

 (figs. 7 and 8, pi. syn.). 



The syncytium is now much more vascular than in Stage B, 

 numbers of enlarged capillaries with distinct endothelial walls 

 occurring throughout the protoplasm. As in Stage B, the 

 capillaries are found to enter the syncytium between the 

 lobules. They pass mainly into its superficial zone in order 

 there to ramify just beneath its surface, clothed at this stage 

 by the chorionic ectoderm. 



{b) Syncytium beyond Allantoic Placental Area. — 

 The allantoic placental syncytium at its margin becomes 

 greatly reduced in thickness, and continues on as the syncytium 

 in contact with the vascular omphalopleure (fig. 6, ex. syn.). 

 Here it has a thickness of about '05 mm. It has essentially 

 the same characters as the allantoic placental syncytium. The 

 nuclei are, however, smaller, and stain somewhat less deeply. 

 They are, as a rule, aggregated in nests in the lobules, though 

 here and there they tend to become more irregularly dis- 

 tributed throughout the protoplasm. 



What, however, specially characterises this portion of the 

 syncytium in contact with the vascular area is the richness of 

 its blood-supply. At this stage it is distinctly more vascular 

 than the allantoic placental syncytium. The capillaries form 

 a rich network just beneath and upon its irregular free surface 

 (fig. 6, syn. c). The significance of this fact will be pointed 

 out later, in connection with the description of the vascular 

 omphalopleure. 



Beyond the sinus terminalis, where the syncytium is in 

 contact with the bilaminar omphalopleure, it is on the whole 

 just about half as thick as over the vascular area. Here, 

 though the characteristic arrangement of the nuclei in nests is 

 still to be seen, the nests are small and inconspicuous, and are 

 often separated by fairly wide intervals, in which the nuclei 

 are irregularly distributed in the protoplasm (fig. 6). The 

 nuclei are similar in size and in staining properties to those of 

 the syncytium in contact with the vascular area. The vas- 



