STUDIES IN MAMMALIAN EMBRYOLOGY. 493 



the epithelial layer from which they have sprung. At com- 

 paratively regular distances the cells of the proliferation 

 arrange themselves in a peculiar radiating fashion, leaving a 

 central part without nuclei surrounded by an overcapping 

 layer of nuclei (fig. 69). In transverse sections this arrange- 

 ment of the proliferated cells could be termed fan-shaped, the 

 centre of the fan's radii being situated somewhere in the ute- 

 rine epithelium. 



In the following stages this arrangement becomes converted 

 into a functionally more important one. The centre of the 

 fan-shaped structure becomes an open crypt, the protoplasm 

 breaking up, and the peripheral nuclei forming the epithelial 

 lining of the crypt. The uterine epithelium breaks away from 

 under the crypt, and the inner lining of the crypt solders with 

 the surrounding epithelial surface at the lower border. All 

 this is figured in detail in figs. 70 and 71 ; whereas figs. 22 

 and 23 elucidate the same processes, and at the same time the 

 comparative thickness of the proliferation as compared with 

 the connective tissue and muscularis of the uterine wall. These 

 figures, compared with figs. 17 and 19, undeniably show that 

 the connective tissue has also increased in bulk. The open 

 crypts, secondary derivates of the epithelial proliferation, are 

 now spread over the concave surface where the placenta is 

 going to develop. Between the openings of these crypts the 

 mouths of the uterine glands are situated. It is not as diffi- 

 cult as it would perhaps seem to be to recognise a gland from 

 the newly formed crypts. Figs. 21 and 68 make this clear; 

 especially when the latter is compared to fig. 71, the well-defined 

 glandular epithelium is ever so much more distinct than the 

 epithelium of the crypt, which as yet is only sharply circum- 

 scribed where it passes into the surface layer (fig. 71) and 

 encloses a distinct lumen. 



This lumen of the crypt becomes clearly circumscribed — 

 and with it the boundaries of the cells lining the crypts — in 

 the now following stages of figs, 24, 25, and 74. 



The proliferation process has here reached its maximum de- 

 velopment ; its products, the epithelial crypts, are now ready 



