F. H. A. Marshall 383 



The ferret also differs from most mammals in that it ovulates only after 

 coition (Marshall") and it differs from the rabbit in that no known exceptions 

 to this causal relation have been recorded or observed. The atrophic follicle 

 first figured in 1904 has recently been fully described by Hamilton and Gould." 

 Atresia may set in at all stages of follicular growth and at all times in the 

 cycle. The earliest indications are degeneration of the epithelium and loss 

 of shape. Hamilton and Gould suggest that the interstitial tissue contributes 

 towards the collapse of the follicle by slow cellular proliferation and the 

 pressure which it exerts. The theca becomes fibrotic and constitutes the scars 

 found later in the ovaries. Unlike that of the ground squirrel mentioned 

 above, the zona pellticida of the ovum may persist for a long time along with 

 some leucocytes which remain in the cavity. This description is in general 

 agreement with my own earlier but less detailed observations. Hamilton and 

 Gould state further that the scars of the atrophic follicles of the ferret differ 

 from those of the sow, goat, and mouse in which there is proliferation of the 

 theca that comes to fill the collapsed cavity with fibrous ingrowth, whereas in 

 the ferret there is comparatively little active proliferation of the theca. There 

 is often, however, a loose ingrowth of connective tissue, which may be seen 

 while the ovum is still visible in the cavity (MarshalP"). No hemorrhage from 

 the theca or any part of the wall of the follicle was ever observed, and this may 

 be interpreted as due to the greater density of the tissue as compared with that 

 of the rabbit. 



Unruptured follicles of a somewhat different type have also been observed 

 in the ferret in some cases where the animals had been on heat for an ex- 

 ceptionally long time. These show a retention with lutealization of some of the 

 epithelial cells not unlike those of the rabbits described above. The ova in 

 various stages of degeneration could also sometimes be seen within such 

 follicles. 



An attempt was made to discover if there were differences in the histological 

 appearance of the ovary at different times in the prolonged heat periods. For 

 this purpose ferrets were killed after they had been continuously on heat under 

 natural conditions (that is, without artificial stimulation by light or electricity) 

 for five, six, eight, and twelve weeks. It may be stated at once, however, that 

 there was general resemblance in the ovarian histology at all those stages. Each 

 stage showed large follicles, some apparently ready to rupture, but there were 

 no discharged follicles or typical corpora lutea. There were also follicles in 

 process of degeneration, but in the five- and six-week stages these were small 

 ones which apparently had never grown. In the ferret which had been on heat 

 for eight weeks the ovaries contained some medium-sized atrophic follicles 

 with the degenerate ova surrounded by unenlarged or only slightly enlarged 

 epithelial cells. Big degenerate follicles with lutealization of some or most of 

 the epithelial cells as described above were found only in the twelve-week 

 stage. The observations made were not numerous enough to warrant any very 

 definite conclusions, but they suggest that degeneration of large follicles is 



