132 T. THOMSON FLYNN 



almost intact throughout. At certain localized points, however, 

 the ectodermal cells are deeper than the average. Some cells 

 have become multinucleate and the nuclei are in many cases 

 situated basally, such cells being deepened considerably com- 

 pared with their original condition. Below the ectoderm the 

 syncytial nuclei are arranged in their lobules. These nuclei 

 are rounded, and although membranate the chromatic contents 

 are spare. Each nucleus contains usually n well-defined 

 nucleolus. Examination of the syncytial nuclei of the extra- 

 placental area shows that the suppression of the chromatin 

 contents and the presence of a single rounded nucleolus is 

 a general characteristic. Even with iron-haematoxylin staining 

 only a very faint network can be made out. It is quite other- 

 wise with the nuclei of the cells of the ectoderm layer. A refer- 

 ence to Hill's PI. XXX, fig. 9, will serve to show that the nuclei 

 of these cells contain quite a well-developed chromatin network 

 with a number of karyosomatic aggregations, even as many as 

 half a dozen in some cases. Further, these nuclei are seldom 

 spherical, but irregularly ellijitical, o^'alish, or lenticular, and 

 generally of large size. 



The difference in shape and histological characteristics 

 between these and the sjmcytial nuclei is most marked, and 

 in my preparations they can immediately be distinguished from 

 one another. 



Bearing in mind, then, the difference between the rounded, 

 bead-like, maternal sj^ncytial nuclei — ' typical resting nuclei '• — 

 now congregated in groups in the syncytial lol)ules whether 

 within or without the placental area — and the more robust 

 layer of irregularly-shaped nuclei of the foetal ectoderm, each 

 with its network of easily-stained chromatin, it will be possible 

 to follow out their migration and rearrangement in a general way. 



In Hill's PL xxix, fig. 7, which represents a marginal 

 portion of the placental area with the chorion attached (embryo 

 7 mm.), the foetal ectoderm {ch.ect.) is apparently complete 

 and unbroken, while on the lower side of the figure are 

 the syncytial lobules containing groups of syncytial nuclei. 

 Between these two sets of elements are to be seen a number of 



