566 OVULAT1ON AND FUNCTION OF MENSTRUATION. 



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

 as well as its formation, is independent of sexual intercourse. 



Continued observation shows this to be the case, also, in the 

 viviparous quadrupeds. The researches of Bischoff, Pouchet, and 

 Coste have demonstated that in the sheep, the pig, the bitch, the 

 rabbit, c., 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 show that Graafian vesicles have matured, rup- 

 tured, and discharged their eggs, in the same manner as though 

 sexual intercourse had taken place. Sometimes the vesicles are 

 found distended and prominent upon the surface of the ovary; 

 sometimes recently ruptured and collapsed ; and sometimes in vari- 

 ous stages of cicatrization and atrophy. Bischoff, 1 in several in- 

 stances of this kind, actually found the unimpregnated eggs in the 

 oviduct, on their way to the cavity of the uterus. In those animals 

 in which the ripening of the eggs takes place at short intervals, as, 

 for example, the sheep, the pig, and the cow, it is very rare to exa- 

 mine the ovaries in any instance where traces of a more or less 

 recent rupture of the Graafian follicles are not distinctly visible. 



One of the most important facts, derived from the examination 

 of such cases as the above, is that the ovarian eggs become deve- 

 loped and are discharged in successive crops, which follow each 

 other regularly at periodical intervals. If we examine the ovary 

 of the fowl; for example (Fig. 180), we see at a glance how the eggs 

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

 instance, the process of evolution is very 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, firmer, 

 somewhat opaline, and yellowish in hue ; and finally those which 

 are fully developed, opaque, of a deep orange color, and just ready 

 to leave the ovary. 



It will be observed that in this instance the difference between 

 the undeveloped and the mature eggs consists principally in the 

 size of the vitellus, which is furthermore, for reasons previously 

 given (Chap. III.), very much larger than in the quadrupeds. It 

 is also seen that it is the increased size of the vitellus alone, by 

 which the ovarian follicle is distended and ruptured, and the egg 

 finally discharged. 



1 Memoire sur la clinte periodique de 1'oeuf, &c , Annales des Sciences Naturelles, 

 A out Septembre, 1844. 



