404 THE PHYSIOLOGY OF REPRODUCTION 



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 x 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 carbo- 

 hydrate for the foetus. In man also the decidual cells contain 

 glycogen at an early period. Pat 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-metabolism of the foetus require further study. 



PART II 



THE FIRST STAGES OF PREGNANCY: PLACENTAL 

 CLASSIFICATION 



I. THE OVARIAN OVUM 



WHILE still in the ovary, the ovum obtains the necessary nutriment 

 by means not yet discovered. In the Graafian follicle it is surrounded 

 by the zona pellucida and externally the corona radiata. 2 The origin 

 of the zona pellucida has been variously described. According to 

 some authorities it is the thickened outer edge of the ovum itself, 

 a true vitelline 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 stripe are seen 

 running from without inwards. Their appearance indicates the 

 possibility that they are pores or delicate canals by which protoplasmic 

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

 may reach the ovum and nourish it (see p. 121). Whatever the 

 source of the food-supply of the ovum is, it not only increases in size 

 until it is ripe for deliverance, but stores in its protoplasm yolk 

 granules, the deutoplasm of Beneden, which increase in number as the 

 ovum approaches maturity. The granules vary in size and number 

 in different species, and also in their position. They may be mingled 

 uniformly through the cytoplasm, or be collected at the marginal 

 zone (sheep), or at the periphery of thfe central zone (man). During 

 the earliest stages of segmentation, when perhaps food is not readily 



1 Nattan-Larrier, " Fonction secretaire du placenta," Comp. Rend, de VAcad. 

 de Sc., vol. lii., 1900. 



2 Or zona radiata, i.e. the innermost layer of follicular epithelium and within 

 the discus proligerus. 



