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B. LOFTS and R. K. MURTON

Summary.

A single intra-muscular dose of cadmium chloride (0·2 ml of a 0·04 m solution) caused a retardation of the photoperiodic response in the testes of wood-pigeons (C. palumbus) given a 16-hr photoperiod in late February to March. A similar injection administered in August did not affect the normal seasonal post-nuptial regression. Necrosis of the seminiferous tubules was not evident.

An intra-muscular injection given to feral pigeons (C. livia) with testes in full breeding condition, again produced no necrosis of the seminiferous tubules, but interfered with the radial co-ordination of cells in the germinal epithelium.

An intra-testicular injection (0·1 ml of 0·04 m solution) of cadmium chloride into specimens of both species, caused localized necrotic damage as well as a more general disruption of germ-cell co-ordination in the seminiferous epithelium.

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B. LOFTS, R. K. MURTON and R. J. P. THEARLE

In recent years, attention has been focused on the potential of reproduction inhibitors for the possible control of harmful birds (Davis, 1961, 1962; Elder, 1964; Becker, 1966). Elder, in his search for an effective avian oral contraceptive, found that the best results were obtained with a hypocholesterolemic agent, 22,25-diazacholesterol dihydrochloride (compound SC-12937, Searle & Co., Chicago). When this constituted 0·1% of the diet of pigeons for 10 days, ovulation was inhibited for 3 months and impaired for a further 3 to 9 months. The present study was designed to investigate the effects of compound SC-12937 on the pre-incubatory behaviour of Columba livia and to assess the action of the drug on normal testis cytology.

Males and females in two groups, each of

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H. W. TSUI, W. H. TAM, B. LOFTS and J. G. PHILLIPS

Summary.

The seasonal changes in the capacity of the testicular tissue of the masked civet cat, Paguma l. larvata, to produce testosterone from radioactively labelled pregnenolone in vitro, has been measured chromatographically, together with an analysis of the spermatogenic cycle and the lipid cycle of the interstitial Leydig cells.

Testosterone is the main androgen produced by the civet cat testis in vitro and its production, assessed as a percentage conversion from the precursor added, closely follows the interstitial lipid cycle and seasonal spermatogenic cycle, reaching a peak in March and rapidly declining at the end of the reproductive season. The most active period of testosterone production takes place at a time when the interstitial cells are becoming rapidly depleted of their lipids, and the very rapid decline which takes place in July is marked histochemically by the interstitial tissue entering a heavily lipoidal end-phase.

The possible relationship between the seasonal histochemical events and the rate of androgen synthesis is discussed.