UTERINE NUTRITION. 525 



temporary stomach of the embryo. Its wall constitutes the germinal 

 membrane, upon which the embryo arises. New cells being constantly 

 added, the membrane increases in thickness ; and here it may ^he germinal 

 be remarked that, in most types, the yolk is to be considered membrane, 

 as presenting two portions the germ-yolk and the food-yolk ; the for- 

 mer being immediately employed in the development of the embryo, and 

 the latter being a stock for more advanced supply. In mammals, for 

 whom other means of nutrition are quickly provided, the food-yolk is im- 

 perceptible, and, moreover, in them the albuminous coating of the zona 

 pellucida is small ; but in birds, the embryo of which has to be nourish- 

 ed independently of the parent, the quantity is necessarily large. As we 

 have sai'd, this albuminous covering and the zona together constitute the 

 chorion, the exterior of which presents a rugged aspect, from the appear- 

 ance of absorbing radicles, which, becoming imbedded or dove- 

 tailed in the deciduous membrane, presently to be described, 

 establishes the necessary connection for tuft nutrition, and thereby ob- 

 taining albumen from the parent. 



III. Fertilized Ovum in the Uterus. 



While the ovum is passing through the Fallopian tube or oviduct, it 

 obtains a coating of albuminous material outside of its zona pellucida, as 

 has been said. This coating becomes the means of attachment to the 

 uterus, and thereby of the absorption of nutriment in the following way. 

 The outside surface of the incipient chorion presents a layer of cells, 

 and soon after assumes a fibrous structure. In this condi- uterine nutri- 

 257. tion the ovum makes its appearance in tion - 



the uterus, on the interior of the surface of which the 

 mouths of a great number of follicles open. These 

 follicles are not unlike those which the stomach 

 presents. Their general appearance is illustrated by 

 Fig. 257; d, csecal terminations of glands; e, their 

 tubes ; , mouths on interior of uterus. The con- 

 stitutional disturbance which is at this time taking 

 place, enhanced by the presence of the ovum in the 

 organ, at once increases its vascularity ; the follicles 

 become larger, cells are abundantly developed in 

 them, and the uterine cavity is filled with a liquid 

 containing many nucleated cells. This plastic semi- 

 fluid material receives the fringes of the villous coat 

 of the chorion, which are now being developed ; and 

 these even find their way into the mouths of the 

 ** glandular tubes ; from this exudation or secretion 

 uterine tubes. the membrana decidua forms, though by some it is 



