PEB10DICAL OVULATION. 563 



CHAPTER V. 



OX PERIODICAL OYULATION, AND THE FUNCTION 

 OF MENSTRUATIO 



I. PERIODICAL OVULATION. 



WE have already spoken in general terms of the periodical ripen- 

 ing of the eggs and their discharge from the generative organs of 

 the female. This function is known by the name of " ovulation," 

 and may be considered as the primary and most important act in 

 the process of reproduction. We shall, therefore, enter more fully 

 into the consideration of certain particulars in regard to it, by 

 which its nature and conditions may be more clearly understood. 



1st. Eggs exist originally in the ovaries of all animals, as part of 

 their natural structure. In describing the ovaries of fish and reptiles 

 we have said that they consist of nothing more than Graafian vesi- 

 cles, each vesicle containing an egg, and united with the others by 

 loose areolar tissue and a peritoneal investment. In the higher 

 animals and in the human subject, the essential constitution of the 

 ovary is the same ; only its fibrous tissue is more abundant, so that 

 the texture of the entire organ is more dense, and its figure more 

 compact. In all classes, however, without exception, the interior 

 of each Graafian vesicle is occupied by an egg ; and it is from this 

 egg that the young offspring is afterward produced. 



The process of reproduction was formerly regarded as essentially 

 different in the oviparous and the viviparous animals. In the ovipa- 

 rous classes, such as most fish, and all reptiles and birds, the young 

 animal was well known to be formed from an egg produced by the 

 female ; while in the viviparous animals, or those which bring 

 forth their young alive, such as the quadrupeds and the human 

 species, the embryo was supposed to originate in the body of the 

 female, by some altogether peculiar and mysterious process, in 

 consequence of sexual intercourse. As soon, however, as the 

 microscope began to be used in the examination of the tissues, 



