EGG AND FEMALE ORGANS OF GENERATION. 689 



swells into a transparent gelatinous mass, in which the eggs are sepa- 

 rately imbedded. Jt supplies, by its subsequent liquefaction and ab- 

 sorption, a certain amount of nutritious material, for the development 

 and growth of the embryo. 



In the scaly reptiles and in birds, the oviducts perform a more im- 

 portant function. In the common fowl, the ovary consists, as in the 

 frog, of follicles, loosely united by connective tissue, and containing eggs 

 in different stages of development (Fig. 226, ). As the egg which is 

 approaching maturity enlarges, it distends the cavity of its follicle, and 

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

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

 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 discharged from the 

 lacerated opening. 



At the time of 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 underneath the 

 vitelline membrane, at one point upon the surface of the vitellus, is a 

 round white spot, consisting of a la}'er of minute granules, termed the 

 " cicatricula," in which the germinative vesicle is 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 disappeared; but the 

 cicatricula is still an important part of the vitellus, and it is from this 

 spot that the body of the chick begins afterward to be developed. 



As 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 embraced by the upper expanded extremity of this tube, 

 and commences its passage downward. In the fowl, the muscular coat 

 of the oviduct is highly developed, and its peristaltic contractions urge 

 the egg from above downward, somewhat in the same manner as the 

 oesophagus or the intestines transport the food in a similar direction. 

 While passing through the first five or six centimetres of the oviduct 

 (c, d), where the mucous membrane is smooth and transparent, the 

 yolk absorbs a certain quantity of fluid, becoming consequently rather 

 more flexible and yielding in consistency. It then passes into a second 

 division of the generative canal, in which the mucous membrane is 

 thicker and more glandular, and is thrown into longitudinal folds. 

 This portion of the oviduct (d, e) extends over about 22 centimetres, 

 or more than one-half its entire length. In its upper part, the mucous 

 membrane secretes a viscid material, by which the yolk is incased, 

 and which soon consolidates into a gelatinous deposit, thus forming a 

 second envelope, outside the vitelline meihbrane. 



The peristaltic movements of this part of the oviduct are such as to 

 give a rotary, as well as a progressive motion to the egg ; and by this 

 means the two extremities of the gelatinous envelope become twisted 

 in opposite directions; forming two whitish looking cords, attached 



