CYCLIC CHANGES IN THE OVARIES AND UTERUS OF THE SOW, ETC. 125 



GROWTH OF THE GRAAFIAN FOLLICLE AND MATURATION OF THE OVUM. 



The ovaries of the large animals are not well suited to the study of the various 

 problems connected with the growth of the Graafian follicle, on account of the 

 obvious physical difficulties which prevent systematic examination of large numbers 

 of follicles and ova. Sufficient information has been gained, however, with respect 

 to the pig, to supply an outline of follicular growth and to correlate its events roughly 

 with those of the oestrous cycle. It appears that normal follicles of maximum size 

 are found only during the period of a few days previous to ovulation. At all other 

 times there is what might be termed a reserve stock of smaller follicles in the ovary, 

 forming a series of all sizes from the microscopic primordial stage to a diameter of 

 about 5 mm. Judging from the evidence of the 22 mature sows mentioned above, 

 it seems that practically all actively functioning ovaries contain a number of follicles 

 of 3.5 to 5 mm. diameter, which are in readiness for the final enlargement which 

 they are destined to undergo just before rupture. Follicles of larger size are usually 

 found to be atretic, although in a few cases there are normal follicles of 6 and even 7 

 mm. diameter during the intercestral period. 



At a time not as yet accurately determined, but which can not be more than 2 

 or 3 days before the onset of oestrus, there begins a rapid enlargement of those 

 follicles which are to discharge their ova, bringing them to a diameter of 7, 8, or 

 even 10 mm.; and at the same time there is a series of histological changes, which, 

 in the smaller animals, have long been known to be connected with the maturation 

 of the ovum. These consist of growth of the theca interna by enlargement of its 

 cellular elements and of a partial dissolution of the cumulus oophorus by separation 

 of its cells, so that the ovum is finally almost freed from its originally firm anchorage 

 to the follicular wall. A full description of these changes will be found in the 

 author's paper of 1919. The ovum itself goes through the first stages of the process 

 of maturation, its nucleus moving toward the periphery of the cell, to form first the 

 typical germinative vesicle, and then to undergo mitosis and extrusion of the first 

 polar body. 



The study of new material has not modified the opinion already expressed in a 

 brief note (1917) that the process of maturation of the ovum follows in the pig 

 the same course as in other mammals. At the moment of rupture of the follicle the 

 first polar body has been discharged and the second polar spindle has been formed, 

 but completion of the second polar body does not take place unless the ovum is 

 fertilized. 



Rupture of all the follicles seems to take place simultaneously or at least 

 within a brief space of time, for in a careful examination of perhaps 200 pairs of 

 ovaries containing recently ruptured follicles there has been only one case in which 

 there were also normal, mature, uncollapsed f ollicles. A few other specimens which 

 appeared to be of this sort proved upon section to be atretic. This conclusion is 

 contrary to that of Ktipfer (1920), who thinks that an appreciable space of time 

 may be required for the rupture of a group of follicles, but the specimens upon which 

 he bases this statement have apparently not been subjected to microscopic exami- 



