OVARY (FUNCTIONS). 



555 



now by Dr. Allen Thomson*, led the former 

 to conclude that the formation of the ovum 

 commences before the existence of the ovisac, 

 the researches of Bischoff point, on the other 

 hand, to the ovisac itself, as the formative or- 

 gan of the ovum. 



The general appearance of the ovisac, when 

 first formed, is that of a pellucid, and often 

 yellowish vesicle, having an elliptic form, and 

 at first so minute as not to exceed -^ TOO'" 

 in diameter ; as, for example, in the ox, the 

 ovary of which animal, according to Barry, 

 would contain in a cubic inch 200,000,000 of 

 such ovisacs. 



The ovisac is more or less pellucid, ac- 

 cording to its size. In the smaller ones, the 

 walls are so transparent as to admit of the 

 form of their granular contents being seen 

 through them (Jig. 377. B, c) ; but as develop- 

 ment advances, they become merely translu- 

 cent. The walls, which are relatively very 

 thick in the small ovisacs, are elastic and dis- 

 tensible, and have an undulating surface, pre- 

 senting numerous depressions, to which is 

 referable the plaited or folded appearance 

 which the contour of the ovisac assumes un- 

 der pressure. 



The ovisac is sometimes formed in the pa- 

 rietes of an already developed Graafian fol- 

 licle ; but whether originating here, or, as is 

 more commonly the case, in the proper sub- 

 stance of the ovary, it is always at first seen 

 lying perfectly loose in a little cavity, exca- 

 vated, as it were, in the substance of the sur- 

 rounding tissues. Subsequently a covering, 

 or tunic, consisting of a rather dense con- 

 nective tissue, susceptible of becoming highly 

 vascular, and closely connected with the ova- 

 rian stroma, is gradually formed upon the 

 outer surface of the ovisac, with which this 

 outer covering now becomes closely united. 

 This is the structure termed by Barry the 

 tunic of the ovisac (Tunica S.theca folliculf). 

 And it is by the union of these two that, 

 according to his observations, the Graafian 

 vesicle is formed. At this stage of its deve- 

 lopment there exist all the elements of the 

 completely-developed follicle, viz., the outer 

 vascular or fibrous coat, the inner softer layer, 

 or proper tunic of the ovisac, and the still 

 more internal epithelial layer of granules re- 

 presenting the membrana granulosa, together 

 with the elements, at least, of the ovum, and 

 the fluid contents of the sac. 



These constitute the most important points 

 regarding the development of the Graafian 

 follicle at the time of its first formation in the 

 Mammalia generally. They serve to facilitate 

 greatly the study of the same parts in Man. 



With regard to the human follicle, the cor- 

 responding stage is most readily observed in 

 the infant, a few months after birth. If at 

 that age a section be made of the ovary, it 

 will be seen to be composed of a parenchyma, 

 which is somewhat lax towards the centre 

 and base, but more dense in the peripheral 

 portion of the organ. The more lax central 



* Page 7C. of this vol., Supplement. 



portion consists of blood-vessels and wavy 

 bundles of connective tissue, the latter being 

 much more distinct in the ovary of the infant 

 than in the adult. The more dense peripheral 

 portion is that in which alone the ova are 

 found. It is made up almost entirely of a 

 mass of minute ovisacs, already containing 

 ova (fig. 373.). 



These ovisacs, at present in a rudimental 

 condition, are of various dimensions. In the 

 example given, their average diameter was 

 5^3 T oVo"- But it happens, occasionally, 

 that ovaries of a very early age are found to 

 contain ovisacs or Graafian follicles of com- 

 paratively large size. Thus, in a specimen in 

 my possession from a child of seven months, 

 one ovary contains a follicle of rather more 

 than V" in diameter, whilst the other is almost 

 entirely occupied by five follicles, the largest 

 of which measures 2%+ \\'", and the smallest 

 is one quarter of that size. In this case the 

 entire length of the ovary is only 7'". 



Second Stage. Growth, Maturation, and Pre- 

 paration for Dclriscence of the Follicle. When 

 the period approaches, or has already arrived, 

 at which an animal becomes apt for reproduc- 

 tion, and is ready to receive the male, a cer- 

 tain number of follicles progressively increase in 

 size, and become more and more superficially 

 placed. Shortly, the more advanced series 

 occupy the surface of the ovary, and present 

 the appearance of round grains close-set, 

 so as to give to the organ sometimes the 

 appearance of a bunch of grapes (fig. 378.). 

 This is more particularly the case in the 

 sow, which affords an excellent example 

 for tracing these changes in the follicle. 



Fig. 378. 



Portion of ovary of the sow. The Graafian follicles 

 project above the surface of the orary. Several, 

 riper than the rest, are conspicuous by their size, a, 

 unripe ; b, riper follicles ; c, stroma. 

 (After Pouchet.) 



Each grain, a, consists of a vesicle filled 

 with a limpid fluid, albuminous, viscid to 

 the touch, of a slightly yellow colour, arid 

 coagulable by heat and alcohol. Their walls, 

 previously diaphanous, now become opaque 

 from the thickening of the inner membrane of 

 the vesicle, i. e., of the ovisac itself. From 

 four to six of these vesicles will be found to 

 become simultaneously developed in each 

 ovary (fig. 378.6, b}. These are always the most 

 superficial. Their form is generally ovoid. 

 They increase until they attain a diameter of 

 about i". 



