ACTION OP THE FEMALE. 



959 



a vesicle of evolution for the ovum, in the same way that the gland-cells of the 

 testis act as vesicles of evolution for the spermatozoa. The development of 

 ovisacs commences at a very early period of life ; in the ovaries of some animals, 

 they can be detected almost as soon as these organs are themselves evolved ; and 

 in all, they show themselves soon after birth. In Fig. 4 (Plate I.), is repre- 

 sented the condition of the Graafian vesicles in various stages of development, 

 as they are seen imbedded in the fibrous stroma of the ovarium, in a thin slice 

 from the ovary of a sow three weeks old ; by which time the germinal vesicle, 

 which is the first part of the ovum that makes its appearance, has been developed 

 in their interior. The germinal vesicle, which distinctly shows the germinal 

 spot, is surrounded by an assemblage of granules, which is the first indication 

 of a yelk; and around these the zona pellucida appears to be subsequently 

 developed. The Ovum at first occupies the centre of the Graafian vesicle, but 

 it subsequently removes to its periphery; and, when the contents of the ovisac 

 are undergoing maturation, prior to their escape, the ovum is always found on 

 the side of it nearest to the surface of the ovary. The proper ovisac, whose 

 wall is formed of a non-vascular membrane, is surrounded by a vascular layer, 

 which is formed by a condensation of the ordinary stroma of the ovarium ; it is 

 this, which is reckoned as the outer layer of the Graafian vesicle. 



964. A continual change seems to be taking place in the contents of the 

 ovarium, during the greater part of life; certain of the ovisacs or Graafian 

 vesicles, and their contents, successively arriving at maturity, whilst others 

 degenerate and die. According to the valuable inquiries of 



Dr. Ritchie, 1 it appears that, even during the period of child- Fig. 243. 



hood, there is a continual rupture of ovisacs and discharge of 

 ova, at the surface of the ovarium. The Ovaria are studded 

 with numerous minute copper-colored maculae, and their 

 surface presents delicate vesicular elevations, which are 

 occasioned by the most matured ovisacs; the dehiscence of 

 these takes place by minute punctiform openings in the 

 peritoneal coat, and no cicatrix is left. At the period of 

 puberty, the stroma of the ovarium is crowded with ovisacs ; 

 which are still so minute, that in the Ox (according to Dr. 

 Barry's computation) a cubic inch would contain 200 millions. 

 of them. The greatest advance is- seen in those which are 

 situated nearest the surface of the Ovarium; and in such 

 the Graafian vesicle, with its two coats, may be distinctly 

 traced. In those animals whose aptitude for conception is 

 periodical, the development of the ova to such a degree that 

 they become prepared for fecundation is periodical also. 

 This development is made evident, when the parts are ex- 

 amined in an animal which is " in heat/' by the projection 

 of the Graafian vesicles from the surface (Fig. 243) ; and it 

 consists not merely in an increase of size, but in certain ovariumofthetfa&&#, 

 internal changes presently to be described. at the period of Heat; 



965. In the Human female, the period of Puberty, or showing various stages 

 of commencing aptitude for procreation, is usually between of the extrusi n of ova. 

 the 13th and 16th years; it is generally thought to be 



somewhat earlier in warm climates than in cold, 3 and in densely populated 



1 "London Medical Gazette," 1844. 



2 It has been stated, by almost all physiological writers, that women (like fruits) reach 

 maturity and that menstruation commences much earlier in hot climates, particularly 

 between the tropics, than in temperate and very cold countries ; from many elaborate and 

 interesting papers which have been published within a few years, however, especially from 

 those of Mr. Roberton, of Manchester (recently collected in his "Essays on Menstruation, 



