140 GEORGE W. CORNER 



a sign, for the formation of the polar bodies, as was pointed out 

 by Flemming ('85), is a frequent occurrence in early atresia. 

 As atresia may set in at any time in the life of a follicle, even up 

 to the last, it is obvious that we can never state with complete 

 assurance whether a given Graafian follicle is doomed to degen- 

 eration or is about to rupture and give rise to a corpus luteum. 



We shall probably not be in error, however, in assuming that a 

 follicle is normal and mature if it is taken from the animal at a 

 time when ovulation is known to be imminent, and if it contains 

 a normal ovum in which the process of maturation is under way. 



To satisfy these requirements is easy when the animal is small 

 enough to be under observation in the laboratory, when an im- 

 pending ovulation can be predicted (as, for instance, in the rat 

 and mouse, which are now known to ovulate about eighteen 

 hours after littering) and when the small size of the ovaries and 

 tubes readily permits serial sectioning. In animals like the hog, 

 however, it is more difficult to observe these two criteria of the 

 mature follicle, and no previous investigators of this species 

 have watched the animal during life in order to determine the 

 imminence of ovulation, nor have any taken the pains to find 

 and study the ova of the follicles which they described as ripe. 



In the author's material, of sixteen animals known to have 

 been in heat when killed, only two were taken early enough in 

 oestrus to contain unruptured follicles. In one, all the follicles 

 were still unruptured. Three of them were successfully sectioned ; 

 two of them contained ova with nuclei presenting 'germinal 

 vesicles,' the third showed the first polar body and the second 

 polar spindle. In the second sow, one of the follicles had rup- 

 tured; the tubal ovum could not be found; one of the remaining 

 follicles, upon sectioning, showed its ovum to be in the matured 

 state, with the second polar spindle formed. There can be little 

 doubt, therefore, that the follicles in question were perfectly 

 normal and would have immediately shed their ova and devel- 

 oped into corpora lutea had the sows not been slaughtered. 



These follicles possessed clear, translucent, almost spherical 

 walls, protruding a great part of their bulk from the ovary, as is 

 characteristic of the species. They all measured about 7 mm. 



