THE PLACENTATION OF PEBAMELES. 403 



cularity of this region is considerable, but much less so than in 

 the syncytial region in relation to the vascular omphalopleure. 



II. FcETAL Membranes. — [a) Chorionic Ectoderm. — 

 The ectodermal cells of the discoidal area of allanto-chorion 

 are at this stage found firmly adherent to that portion of 

 the syncytium we have already described under the term 

 allantoic placental. 



The chorionic ectoderm consists of a single layer of irregu- 

 larly columnar or cubical cells, of large size and with large 

 ovalish or rounded deeply staining nuclei (figs. 6, 7, and 8, ch. 

 ect.). The layer is on the whole sharply marked off from the 

 underlying syncytium by the fact that the protoplasm of the 

 ectoderm cells stains much less deeply than tlie syncytial 

 protoplasm. The outer ends of the ectoderm cells project quite 

 irregularly, and are found to be accurately adapted to the 

 irregular syncytial surface, dipping down into and filling up 

 every little depression in its surface. The connection, then, 

 between the chorionic ectoderm and the underlying syncytium 

 is of the closest and most intimate character. Such close and 

 accurate apposition could only have arisen through a mutual 

 process of growth and enlargement, affecting both the ectoderm 

 cells themselves and the underlying syncytium. 



So far the above description of the chorionic ectoderm would 

 apply to the whole of that layer in a stage slightly earlier than 

 the one under consideration. In this latter, however, the 

 ectoderm is not uniform in character over its whole extent, 

 since over certain portions of it degenerative processes have 

 already set in. Such a portion is represented in fig. 9. It 

 will be there seen that the ectoderm no longer forms a con- 

 tinuous and uninterrupted layer of fairly regular cells, but is 

 irregular and definitely interrupted on the right side of the 

 figure, thus allowing the allantoic capillaries to come into direct 

 contact with the vascular syncytium. A comparison of the 

 chorionic ectoderm in fig. 8 {ch. ect.) with that shown in this 

 fig. 9 will render at once apparent the marked changes which 

 have taken place in the characters of the cells. Here they are 



