600 REPRODUCTION. 



provided for in the same manner with that of other parts of the bodily 

 structure. 



2. The ovarian eggs become more fully developed at a certain age 

 when the generative function is about to be established. During the 

 early periods of life, the ovaries and their contents, like many other 

 organs, are imperfectly developed. They exist, but they are as yet inca- 

 pable of functional activity. In the young chick, the ovary is small ; 

 and the eggs, instead of presenting a voluminous, yellow, opaque vitel- 

 lus, are minute, transparent, and colorless. In young quadrupeds, and 

 in the human female during infancy and childhood, the ovaries are 

 equally quiescent. They are small, friable, and of nearly homogeneous 

 appearance to the naked eye ; presenting none of the enlarged follicles, 

 filled with transparent fluid, which afterward become a characteristic 

 feature of their structure. At this time, accordingly, the ovaries are 

 inactive, the eggs which they contain immature, and the female inca- 

 pable of bearing young. 



But at a certain period, which varies in the time of its occurrence 

 in different species, the sexual apparatus enters upon a state of activity. 

 The ovaries increase in size, and their eggs, which have previously 

 remained quiescent, take on a rapid growth, the structure of the vitellus 

 being completed by a deposit of semi-opaque granular matter in its 

 substance. In this condition, the eggs are ready for impregnation, and 

 the female becomes capable of bearing young. She is then said to have 

 arrived at the state of "puberty," in which the generative organs are 

 fully developed. This change is accompanied by a corresponding altera- 

 tion in the system at large. In many birds, the plumage assumes 

 more varied and brilliant colors ; and in the common fowl, the comb, 

 or " crest," enlarges and becomes red and vascular. In the American 

 deer (Cervus virginianus), the coat, which during the first year is mot- 

 tled with white, changes in the second year to a reddish tinge. In 

 nearly all species, the limbs become more compact and the body more 

 rounded ; and the whole external appearance is so altered as to indicate 

 that the animal has arrived at the period of puberty, and is capable 

 of reproduction. 



3. In the adult female, successive crops of eggs ripen and are dis- 

 charged by rupture of the Graafian follicles. The eggs are not only 

 formed and attain their growth within the ovaries, but they are also 

 ripened and discharged, irrespective of sexual intercourse, from the 

 independent functional activity of the female organism. In many 

 fishes and reptiles, the mature eggs leave the ovary, pass through the 

 oviducts, and are discharged before coming in contact with the sperm- 

 atic fluid of the male. The domestic fowl, if well supplied with nour- 

 ishment, will continue to lay eggs without the presence of the cock ; 

 only these eggs, not having been fecundated, cannot produce chicks. 

 In oviparous animals, therefore, the discharge of the egg, as well as 

 its formation, may take place independently of sexual intercourse. 



This is also true of the vivipara. The observations of Bischoff, 



