384 Undischarged Ovarian Follicle 



more characteristic of animals which have been on heat for a prolonged 

 period than that it occurs normally in all estrous ferrets. Such a view is con- 

 sistent with what was found in a ferret subjected to ultraviolet light for 

 thirty-eight weeks, but it is to be noted that in this case no degenerate ova 

 were found in the follicles (Marshall'^. These observations suggest that in 

 the ferret, as in the rabbit, ripe follicles develop in relays and then degenerate 

 if ovulation cannot occur, as described for the rabbit by Smelser, Walton 

 and Whetham,^ but that the process does not go on so rapidly in the ferret. 



Attempts were made to induce ovulation in the ferret by electrical stimula- 

 tion through the head by the method which produced ovvdation or the forma- 

 tion of hemorrhagic follicles in the rabbit (Marshall and Verney'^). With 

 ferrets, however, no reaction on the ovaries was obtained. These negative 

 results may have been due to the stimulation not being applied for a suffi- 

 ciently long period, since ferrets in copulating normally take a very long time 

 over the process, and if the male is withdrawn after a quarter of an hour ovula- 

 tion may not follow. Or they may have been due to the fact that the electrical 

 resistance of the bones of the ferret's skull is greater than that of the rabbit's, 

 and since the electrodes were external to the cranium less current would pass 

 through to the hypothalamus and pituitary (Harris"). With these considera- 

 tions in mind Harris stimulated the hypothalamus directly with an electrode 

 inserted into the posterior region. As a result at post-mortem 102 hours after 

 stimulation three cystic follicles with extensive lutealization were found in 

 the ovaries, but no blood follicles. 



Summary 



(1) Among all the mammals in which the reproductive processes have been 

 investigated the rabbit appears to be unique in having ovarian blood follicles 

 as a frequent phenomenon. 



(2) Ferrets do not ovulate or develop blood follicles (as do rabbits) when 

 experimentally stimulated, possibly on account of the denseness of the tissue 

 surrounding the follicles. 



(3) Histological study of feirets' ovaries suggests that in this animal, as in 

 the rabbit, ripe follicles develop in relays in the ovaries during estrus, but 

 that in the ferret the process is more marked towards the later stages of the 

 prolonged heat periods. 



(4) Appearances suggest also that especially in the later stages of estrus the 

 ripe follicles become atrophic, some of the epithelial cells at first becoming 

 hypertrophied while the ovum remains in the cavity of the follicle. 



REFERENCES 



1. Marshall, F. H. A.: Biol. Revs. 17:68, 1942. 



2. Heape, W.: Proc. Roy. Soc. London, s,B 76:260, 1905. 



3. Hammond, J.: Reproduction in the Rabbit (Edinburgh: 1935). 



4. Robson, J. M.: Recent Advances in Sex and Reproductive Physiology (2d ed.; London: 



1940). 



