Cyclic changes in the reproductive organs of male mammals have been studied in a few forms only, but the information available reveals interesting differences in the duration of reproductive activity, and in the correlation between the various organs. Marshall (1911) has described the reproductive cycle in the male hedgehog. Regaud (1904), Tandler and Grosz (1911) and Lecaillon (1909) have studied the mole, but with conflicting results. Rasmussen (1917 and 1918) gives detailed information of the periodic changes in the interstitial tissue of the testis in the woodchuck, and more recently Courrier (1923) has investigated the reproductive cycle in various bats, in the mole, hedgehog, and marmot. The work of Marshall (1904), Robinson (1918) and Hammond and Marshall (1930) has established that in the female ferret the breeding season is restricted and lasts from April to August ; during the remaining months of the year the reproductive organs are in a state of quiescent anœstrus. The first mating occurs in March or April. The present investigation was undertaken in order to determine the duration of the quiescent period in the male ferret and to compare the changes in the testis tubules with those in the interstitial tissue and accessory organs. The condition of the reproductive tract has accordingly been studied at various times of the year, and an attempt has been made to assess the changes in the organs and in their constituent parts.

Cadmium chloride, in a single subcutaneous injection, can destroy spermatogenic and interstitial cells in the rat testis (Pa\l =r%v\\l =i ' \zek,1957) and produce changes in the pituitary. The interstitial tissue is restored by ingrowths from the tunica and full androgen secretion returns before there is any regeneration of germinal epithelium.A cytological study has been made of the peripheral and central pituitary gonadotrophs; the latter revert almost to normal as the interstitial tissue regenerates, whereas the former retain characteristic castration features, unless there is also regeneration of the germinal epithelium. This seems to indicate that in the normal testis there is a hormone contribution from the seminiferous tubules as well as from the interstitial cells.The long-term effects of cadmium on the testis depend on the dose. Early stages of tubule restoration have been studied, but after administration of 0\m=.\9 mg., actual proliferation of the germinal epithelium was rarely found \p=m-\only in four out of twenty rats, 113 or 142 days after injection.

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