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It has been shown by Smith and Engle ('27) and Zondeli and Aschheim ( '27) that implantation of anterior-lobe tissue into immature female rats or mice stimulated the ovaries of these small animals to activity and a precocious sexual maturity resulted. Furthermore, Smith and Engle demonstrated that the anterior-lobe tissue of immature rats contains amounts of the ovarian-stimulating hormones equal to those found in mature rats. The experiments of Smith and Engle demonstrate that the ovarian-stimulating hormones are present in the anterior pituitaries of immature rats, but, for reasons as yet unknown, these factors either are not released into the blood stream or do not become functionally active in the intact animal until the time of puberty.We have carried out a comparative study in which we have tested the capacity of anterior-hypophyseal tissue, taken from mature and immature female rabbits, to induce ovulation in sexually mature rabbits. The technical procedures were as follows. The donor animal was anaesthetized with ether and then bled to death. The anterior lobe of tho hypophysis was removed and weighed. It was then ground with a small amount of sand in sterile saline; the resulting mixture was centrifuged for twenty minutes and the super-

A considerable number of investigations have been published which have demonstrated that the anterior lobe of the hypophysis plays an important rBle in the physiology of the female reproductive system. Some of these studies have shown not only that the hypophysis is an important part of

Since this paper is the fourth paper of a group in which we have considered cyclic histological changes in the anterior pituitaries of dogs, sows, rats and rabbits, it seems desirable that we summarize and correlate our findings in these different species. For this reason, we have reviewed in some detail the cyclic histological changes occurring in the anterior lobe of the hypophysis of the dog (Wolfe, Cleveland and Campbell, '32 and '33), of the rat (Wolfe and Cleveland, '33) and of the sow (Cleveland and Wolfe, '33). Previous to the appearance of these papers, cyclic histological variations had been described in the anterior hypophysis of the woodchuck (Rasmussen, '21) and of the rat (Haterius and Charipper, '30, and Reese, '32).Early in the studies on the cyclic changes occurring in the anterior hypophysis, it was found that there were certain differences in the histology of the anterior pituitary glands of different species. Thus, it was thoughl, advisable to study anterior lobe tissue from several different species of animals exhibiting different types of oestral cycles. I n this way it has been possible to correlate the histological picture presented by the anterior hypophysis of any particular species with the type of oestral cycle exhibited by that species. 'This work has been supported by grants from t f e Committee on Scientific

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