PERIODICAL OVULATION. 705 



3d. Successive crops of eggs, in the adult female, ripen and are dis- 

 charged independently of sexual intercourse. The original formation 

 of the germ, in the bodies of viviparous animals, was formerly sup- 

 posed to be a consequence of sexual intercourse. Even after it became 

 known that the ovaries of these animals contain eggs before impregna- 

 tion, the discharge of the egg from its follicle was thought to occur only 

 under the influence of fecundation ; and the rupture of a follicle was 

 consequently regarded as an indication that sexual intercourse had taken 

 place. 



But subsequent observation showed that not only the existence, but 

 also the ripening and discharge of the egg, are phenomena dependent 

 on the structure and functional activity of the female organism. In 

 many fish and reptiles, the mature eggs leave the ovary, pass through 

 the oviducts, and are discharged externally before coming in contact 

 with the seminal fluid of the male. In the domestic fowl it is a matter 

 of common observation that the hen, if well supplied with nourishment, 

 will continue to lay fully formed eggs without the presence of the cock ; 

 only these eggs, not having been fecundated, are incapable of producing 

 chicks. In oviparous animals, therefore, the discharge of the egg, as 

 well as its formation, may take place independently of sexual inter- 

 course. 



This is also the case in the viviparous quadrupeds. The observa- 

 tions of Bischoff, Pouchet, and Coste, on the sheep, the pig, the bitch, 

 and the rabbit, have demonstated that if the female be carefully kept 

 from the male until after the period of puberty is established, and then 

 killed, examination of the ovaries will sometimes show that Graafian 

 follicles have matured, ruptured, and discharged their eggs, though no 

 sexual intercourse has taken place. Sometimes the follicles are found 

 distended and prominent upon the surface of the ovary ; sometimes re- 

 cently ruptured and collapsed ; and sometimes in various stages of cica- 

 trization and atrophy. Bischoff, 1 in several instances of this kind, found 

 the unimpregnated eggs in the oviduct, on their way to the cavity of 

 the uterus. In species of animals where the ripening of the eggs takes 

 place at short intervals, as in the sheep, the pig, or the cow, it is very 

 rare to examine the ovaries where traces of a more or less recent rup- 

 ture of the Graafian follicles are not distinctly visible. 



One of the most important facts, derived from these observations, is 

 that the ovarian eggs become developed and are discharged in succes- 

 sive crops, which follow each other at periodical intervals. In the ovary 

 of the fowl (Fig. 226), it may be seen at a glance that the eggs grow 

 and ripen, one after the other, like fruit upon a vine. In -this instance, 

 the process of evolution is rapid ; and it is easy to distinguish, at the 

 same time, eggs which are almost microscopic in size, colorless, and 

 transparent ; those which are larger, somewhat opaline, and yellowish 



1 M6moire sur la chQte priodique de 1'oeuf, Annales des Sciences Naturelles, 

 Paris, Aotit Septembre, 1844. 



