654 REPRODUCTION. 



Each villosity then contains a vascular loop, imbedded in its substance, 

 and serving to absorb from the decidua the materials for the growth of 

 the embryo. 



Subsequently, the vascular tufts of the chorion, at first uniformly 

 distributed over its surface, disappear from the greater part of its 

 extent, becoming more highly developed at a particular point, the 

 situation of the future placenta. This is the spot at which the egg is 

 in contact with the decidua vera. Here, both the decidual membrane 

 and the tufts of the chorion continue to increase in thickness and vas- 

 cularity while elsewhere, over the prominent portion of the egg, the 

 chorion not only becomes bare of villosities and comparatively destitute 

 of blood-vessels, but the decidua reflexa, in contact with it, also loses 

 its activity of growth and becomes expanded into a thin layer, with- 

 out any remaining trace of glandular follicles. 



The uterine mucous membrane is therefore developed, during gesta- 

 tion, in such a way as to provide for the nourishment of the embryo 

 in the different stages of its growth. At first, the whole of it is uni- 

 formly increased in thickness (decidua vera). Next, a portion of it 

 grows upward around the egg, and covers its projecting surface (decidua 

 reflexa). Afterward, both the decidua reflexa and the greater part of 

 the decidua vera diminish in the activity of their growth, and lose 

 their importance as a means of nourishment for the embryo ; while 

 that part which is in contact with the vascular tufts of the chorion 

 continues to grow, becoming excessively developed, and taking part in 

 the formation of the placenta. 



