174 



Coneomitantly, changes have been taking place in the inaternal 

 tissues. There had been at a very early period an intense proli- 

 feration of inter-glandular, vasifactive connective tissue in the 

 placental region; siuiultaneously the ducts of the glands begin to 

 degenerate, and their débris is subsequently found, together with 

 isolated raasses of subepithelial tissue, embedded in a tissue lying 

 next the allantoic region of the placenta, and originally supposed 

 by Professor Hubrecht to be of maternal origin. This layer he 

 terined the 'trophospongia', and he described on the outer border 

 of it a layer of phagocytic cells, the 'deciduo-fracts', which 

 ingested maternal nuclei and fragments of chromatin. He now 

 informs me that 'deciduo-fracts' and 'trophospongia' are of em- 

 bryonic origin, that is to say are derived from a portion of the 

 trophoblast which, as in some other forms (Mouse, Guinea-Pig), is 

 never vascularised by the capillaries of the allantois. 



Outside the layer of 'deciduo-fracts' are flattened subepithelial cells, 

 arranged concentrically with the placenta. Next to the trophoblast 

 this layer is looser, and appears reticular, and in between the 

 meshes of this reticulum are rounded vacuolated cells very closely 

 resembling (as I have seen) the maternal glycogen cells of the 

 mouse; but I am unable, of course, to say whether they contain 

 glycogen or not. One of them may be seen in Hubrecht's Fig. 44 D'. 



b.) Sorex. 



In the shrew also the placenta is a concave disc on the anti- 

 mesometric side. The processes attendant upon its formation how- 

 ever exhibit considerable differences from what has been described 

 in the Hedgehog. 



There is a large yolk-sac with a well-developed area vasculosa, 

 which is at first together with the overlying trophoblast closely 

 attached to a ring-shaped thickening of the uterine wall lying 

 immediately mesometrically to the placental region. Later how- 

 ever the yolk-sac with its area vasculosa is pushed away from 

 this thickening by the growth of the hollow allantois, the thicken- 

 ing itself becomiug separated from the wall of the uterus and 

 shed bodily iuto the lumen. 



