PHYSIOLOGICAL PROPERTIES OF GONADS 143 



— and instead of this stage being followed by ovulation the 

 follicles undergo atresia. Figure 12 is a section of a normal rat 

 ovary thirty-six days after birth, and within this one section 

 four atretic follicles (A, B, C, D,) showing a section of the ovum 

 represent quite well the conditions encountered here; in follicle 

 A the ovum has undergone parthenogenetic segmentation, three 

 of the four cells being visible.^ There is, then, a similarity 

 between the ovary before the onset of sexual maturity and the 

 ovarian graft in a male animal, inasmuch as both conditions 

 result in the destruction of the follicles and contained ova instead 

 of the normal processes of ovulation and extrusion of the ovum 

 from the follicles. Figure 7 shows a follicle from a 232-day 

 graft ( male 49 A) in an early stage of its atresia. Here the 

 discus proligerus is undergoing dissolution and the ovum itself 

 is seen to have assumed an elliptical shape instead of the usual 

 rounded condition, and it contains a mitotic figure bearing 

 perfectly definite chromosomes arranged equatorially; it seems 

 possible that this may be the second maturation spindle, at 

 which stage ovulation should intervene, though of this there is 

 no absolute certainty, since the first polar body was not observed. 

 This condition is encountered quite frequently in these grafts, 

 and some twenty-five or thirty ova showing definite spindle and 

 chromosomes have been studied. Figure 8 (from the same 

 graft as fig. 7) is a follicle further advanced in its atresia. Here 

 the discus proligerus has entirely disappeared, excepting possibly 

 the loose scattered cells within the follicular cavity, and the 

 ovum, one piece of which is visible in the section, has undergone 

 fragmentation; in this figure, one can see that the stratum granu- 

 losum is intact and is not undergoing dissolution. It should be 

 emphasized that not one, but scores of cases of fragmentation of 



Fig. 7 Atretic follicle showing ovum in spindle stage (from same graft 

 as figs. 3, 4, and 5). fc, follicular cavity; o, ovum with spindle; St, stratum 

 granulosum. 



Fig. 8 Follicle showing more pronounced atresia (from same graft as figs. 3, 

 4, 5, and 7). fc, follicular cavity; 0, one fragment of degenerating ovum; St, 

 stratum graniilosum. 



^ The nuclei are not well shown in the figure, but they are visible in the prepa- 

 ration, 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 33, NO. 1 



