EGG AND FEMALE ORGANS OF GENERATION. 549 



absorbs the water in which the spawn is deposited, and swells up 

 into a transparent gelatinous mass, in which the eggs are separately 

 imbedded. This substance supplies, by its subsequent liquefaction 

 and absorption, a certain amount of nutritious material, during the 

 development and early growth of the embryo. 



In the terrestrial reptiles and in birds, the oviducts perform a 

 still more important secretory function. In the common fowl, the 

 ovary consists, as in the frog, of a large number of follicles, loosely 

 connected by areolar tissue, in which the eggs can be seen in different 

 stages of development. (Fig. 180, a.) As the egg which is approach- 

 ing maturity enlarges, it distends the cavity of its follicle, and pro- 

 jects farther from the general surface of the ovary ; so that it hangs 

 at last into the peritoneal cavity, retained only by the attenuated 

 wall of the follicle, and a slender pedicle through which run the 

 bloodvessels by which its circulation is supplied. A rupture of the 

 follicle then occurs, at its most prominent part, and the egg is dis- 

 charged from the lacerated opening. 



At the time of its leaving the ovary, the egg of the fowl consists 

 of a large, globular, orange-colored vitellus, or "yolk," inclosed in 

 a thin and transparent vitelline membrane. Immediately under- 

 neath the vitelline membrane, at one point upon the surface of the 

 vitellus, is a round white spot, consisting of a layer of minute 

 granules, termed the " cicatricula." It is in the central part of the 

 cicatricula that the germinative vesicle is found imbedded, at an 

 early stage of the development of the egg. At the time of its 

 discharge from the ovary, the germinative vesicle has usually dis- 

 appeared ; but the cicatricula is still a very striking and important 

 part of the vitellus, as it is from this spot that the body of the chick 

 begins afterward to be developed. 



At the same time that the egg protrudes from the surface of the 

 ovary, it projects into the inner orifice of the oviduct ; so that, when 

 discharged from its follicle, it is immediately embraced by the upper 

 or fringed extremity of this tube, and commences its passage down- 

 ward. In the fowl, the muscular coat of the oviduct is highly deve- 

 loped, and its peristaltic contractions gently urge the egg from above 

 downward, precisely as the oesophagus or the intestines transport 

 the food in a similar direction. While passing through the first 

 two or three inches of the oviduct (c, d), where the mucous mem- 

 brane is smooth and transparent, the yolk merely absorbs a certain 

 quantity of -fluid, so as to become more flexible and yielding in con- 

 sistency. It then passes into a second division of the generative 



