OVARIAN ATRESIA AND PARTHENOGENESIS 45 



of antrum-containing follicles maturing. The paucity of 

 antrum-containing follicles and reduction of atresia is di- 

 rectly noted by Smith and Engle. Finally, the ovulated 

 ova are fertilizable although Engle (19316) found evidences 

 of the degeneration of a number of them in the fallopian 

 tubes. 



An interpretation of the foregoing data is that normally 

 only a limited amount of pituitary secretion is available to 

 the ovary and consequently only a certain percentage of the 

 ova are able to obtain the amount necessary to prevent 

 their atresia, whereas in animals receiving large amounts of 

 pituitary hormones from implants an abnormal number of 

 ova have available sufficient amounts of atresia-suppressing 

 hormones. It cannot be decided, however, whether the 

 effect on the ova is directly exerted by these hormones, or 

 whether the stimulated follicle tissue produces substances 

 ensuring normal ova, or whether some extraovarian sub- 

 stance released into the circulation by pituitary stimulation 

 reacts upon the ova. 



Loeb (1917; see also Meyer, 1913) has indeed suggested 

 that the ovum itself is the controlling factor in follicle 

 development citing the frequent presence of mitoses in fol- 

 licle cells adjacent to the ovum as well as certain histological 

 evidence that the cumulus oophorus develops under the 

 influence of the ovum (Walsh, 1917). Allen and his collab- 

 orators (1924) also maintained that the ovum is the dynamic 

 center of the follicle apparently on the assumption that the 

 mitosis-inducing action of oestrin upon vaginal and uterine 

 epithelium is reflected in the higher mitosis rate in cells 

 adjacent to the ovum becausB the ovum either produces 

 oestrin or induces oestrin formation. In the opossum the 

 presence of many atretic ova is correlated with prolongation 

 of the dioestrus interval (Hartman). This supposed oestrin- 

 ogenic action of the ovum has, however, been largely con- 

 troverted (1) by the discovery of oestrin in corpora lutea 

 as long as two weeks after ovulation (see Allen, 1932) and 

 (2) by the observation that oestrin is produced in x-rayed 



