THE UNDISCHARGED OVARIAN FOLLICLE 



AS IS well known in the matter of ovulation, there are two main categories 

 i\. of mammal, first those in which the mature ovarian follicles discharge 

 spontaneously, usually at or about the periods of estrus, and secondly those in 

 which the follicles rupture normally only as a result of coition or some other 

 sexual stimulus producing an orgasm. The common domestic animals such as 

 the bitch, the mare, the cow, the ewe, and the sow are examples of the first 

 group; the rabbit, the ferret, and the American ground squirrel are examples 

 of the second group. The cat appears to belong to both groups, individuals 

 ovulating spontaneously or only in response to sexual stimulation in about 

 equal proportions. Among the lower vertebrate classes the same physiologi- 

 cal division occurs, but, whereas among birds ovulation generally appears to 

 depend upon the presence of the male, in reptiles, amphibians, and fishes 

 spontaneous ovulation is the rule, though there are some noteworthy excep- 

 tions (MarshalP). With those species of mammal which do not usually ovulate 

 except as a result of coition there are further marked differences in the be- 

 havior of the nonovulating follicles. In the domestic rabbit two types of 

 follicular atrophy are distinguishable. In the commoner type, which with 

 various minor differences is normal for most animals, the liquor folliculi is 

 absorbed, the epithelium is broken down, the ovum becomes flattened and 

 shriveled, and the cavity eventually becomes filled in by a loose ingrowth of 

 connective tissue from the thecal wall. In the second type, which was described 

 by Heape' and Hammond,' there is a large extravasation into the cavity of 

 blood which clots so as to form a red or black spot; this can be seen on the 

 surface, and in the later stages resembles a blood blister in the skin, whereas 

 the other type is visible only microscopically. A newly formed blood follicle 

 is bright red and becomes dark and eventually black only some time after 

 it has been formed. 



I am indebted to Dr. John Hammond for allowing me to examine micro- 

 scopically a large series of blood follicles; these show that in the process of 

 formation the loose tissue of the theca interna has broken down in many 

 places, the previously engorged blood vessels having undergone rupture. The 

 rush of blood into the cavity may result in much of the follicular epithelium, 

 together with the ovum being swept aside and disintegrated, the ovum be- 

 coming shrunken. The latter may, however, remain surrounded at a little 

 distance by a reduced number of epithelial cells. The theca interna may be- 

 come completely or almost completely stripped away from the theca externa, 

 or parts of it may remain lined internally by follicular epithelial walls, some 

 of which are hypertrophied as though in an attempt to form luteal cells. The 

 sections show also various transitional stages between mature follicles and dis- 

 integrated atrophic follicles. In the later stages as described by Hammond' the 

 ovum has disappeared as well as the epithelial cells, and the blood follicle is 



