370 THE PHYSIOLOGY OF REPRODUCTION 



who showed that the spherical globules described by Hofimann 

 were never present in the fresh placenta, but appeared only 

 after its separation, and probably consisted of droplets exuded 

 by the dying chorionic epithelium. It may be mentioned 

 here that the " boules," described by Nattan-Larrier ^ as an 

 internal secretion of the syncytium, have been thought by 

 many to be a post-mortem appearance. 



In Rodents the decidual cells have an important and definite 

 part to play in synthesising and storing glycogen as a supply 

 of carbohydrate for the foetus. In Man also the decidual cells 

 contain glycogen at an early period. Fat globules infiltrate 

 the decidual cells of various animals at a stage when there is 

 no question of a fatty degeneration taking place in the cells. 

 Finally, the cells appear to have the power of ingesting and 

 decomposing erythrocytes, but their relations to the iron- 

 metabohsm of the foetus require further study. 



PART II 



THE FIKST STAGES OF PREGNANCY: PLACENTAL 

 CLASSIFICATION 



I. The Ovarian Ovum 



While still in the ovary, the ovum obtains the necessary nutri- 

 ment by means not yet discovered. In the Graafian foUicle it 

 is surrounded by the zona pellucida and externally the corona 

 radiata. The origin of the zona peUucida has been variously 

 described. According to some authorities it is the thickened 

 outer edge of the ovum itself, a true vitelhne membrane, but it 

 is more probably a deposit from the cells of the corona radiata.'^ 

 Its structure is almost homogeneous, but with the highest 

 powers of the microscope fine striae are seen running from 

 without inwards. Their appearance indicates the possibihty 

 that they are pores or dehcate canals by which protoplasmic 

 processes of the cells of the corona radiata, or a secretion of 



1 Nattan-Larrier, " Fonction s^cretoire du placenta," Comp. Rend, de 

 VAcad. de Sc, vol. lii., 1900. 



^ I.e., the discus proligerus, or innermost layer of follicular epithelium. 



