THE TROPHOBLAST 327 



of the ovum have a marked influence upon the uterine mucosa 

 at the spot where the ovum becomes arrested. The epithelial 

 cells of that mucosa are so acted upon that they become dis- 

 solved and disappear, and the ovum from being on the surface 

 sinks down into a depression, becomes imbedded in the uterine 

 wall, so that now it lies in close apposition to the capillaries 

 underlying the epithelium. These observations have been largely 

 confirmed by my late colleague, Dr. J. C. Webster, now of the 

 University of Chicago. 



This is but the first step in the formation of the placenta. 

 The outer layer or layers of the epiblast of the rapidly growing 

 embryo, termed by Hubrecht the Trophoblast, continues this 

 process of erosion and infiltration in a most remarkable way. 

 This trophoblast literally eats into the maternal tissue opposed 

 to it, forming at first solid cellular processes, purely epiblastic ; 

 later, as the chorionic mesoblast and the allantois with its vessels 

 become developed, these processes gain a mesoblastic and vascular 

 core ; so are evolved the characteristic chorionic villi. Both the 

 more primitive solid processes and the villi, through this phago- 

 cytic, or more truly extra-cellular-digestive, action of the tropho- 

 blast, make their way into the maternal uterine veins and venous 

 sinuses, whereby the cells of the embryo come to lie within the 

 maternal blood-spaces and gain their nourishment, and nourish- 

 ment for the embryo in general, directly from the maternal 

 blood. 



There was for some years violent debate, more especially in 

 Germany, as to the nature of the trophoblast, whether it was of 

 foetal or maternal origin. This culminated in an important 

 debate between anatomists, zoologists, gynaecologists, and 

 obstetricians at the 1897 meeting of the German Naturforscher- 

 versammlung. The most that the most violent opponents of 

 the foetal view can now bring forward is that not all the cells 

 considered by some as trophoblastic, or syncytial, are of foetal 

 origin. Some, they say, are maternal. Nay, more, in the course 

 of a most painstaking and minute study of the development of 

 the rabbit's placenta, my colleague, Dr. Chipman, 1 has shown 

 in a conclusive manner that these trophoblastic or syncytial 



1 IJirough the liberality of the Governors of the hospital, Dr. Chipman's 

 Edinburgh thesis, with its abundant photographic illustrations of this and 

 kindred points, [was] published in the series of Studies from the Royal Victoria 

 Hospital. Montreal [No. 2, 1902]. 



