72 Jeffrey Pudney, Jacob A. Canick, Gloria V. Callard 



measurements have been made, it has been found in some species that, 

 although intratesticular androgen levels are high during spermatogene- 

 sis, the rise in plasma androgen and the display of breeding behavior 

 corresponds to the time of maximal Leydig cell hypertrophy (Courty 

 and Dufaure 1979). These observations, therefore, lead us to the possi- 

 bility that the development of a large volume of Leydig tissue, synthesiz- 

 ing high levels of androgen and estrogen, as for example the glandular 

 tissue of N. lewisi, may be an adaptation for the secretion of steroids 

 into the circulation (see Pudney et al., 1983). The extensive vasculariza- 

 tion of the glandular tissue and the timing of its development following 

 spermiation tends to support this view. The function of these steroids 

 produced by the glandular tissue is unknown, although exceptionally 

 high levels of circulating androgen and estrogen have been measured in 

 N. maculosus (Bolaffi and Callard 1979, 1981). Presumably they stimu- 

 late and maintain development of the secondary sex organs such as the 

 Wolffian ducts, in which spermatozoa are stored prior to mating, as 

 well as the cloacal glands and other spermatophore producing structural 

 paraphernalia. Furthermore, the role any of these steroids plays in the 

 control of behavioral patterns and nuptial coloration resulting in the 

 successful breeding of Necturus can be inferred. Of interest in this 

 respect are reports demonstrating that estrogens in the boar have been 

 shown to be important in conditioning sexual behavior (Joshi and Rae- 

 side 1973). 



The extraordinarily high rate of estrogen production and its func- 

 tion within the testis of Necturus remains, however, obscure. Although 

 some of this estrogen probably affects other body tissues, the presence 

 of receptors in the testis of Necturus maculosus (Mak et al. 1983) indi- 

 cates an action in situ as well. It seems reasonable to predict that estro- 

 gens may exert a direct inhibitory effect on Leydig cell steroidogenesis 

 and thus signal the demise of the glandular tissue, especially since 

 aromatase activity is maximal towards the end of the breeding cycle. A 

 remarkable parallel occurs in the primate corpus luteum, another highly 

 developed glandular tissue in which degeneration (luteolysis) is initiated 

 by direct application of estrogen (Karsch and Sutton 1976). This, inter- 

 estingly enough, brings us back to the original observation by Champy 

 (1913) who suggested that the glandular tissue developed by Necturus 

 was in fact a "corpus luteum of the testis". 



The above account of our studies on Necturus testis raises and 

 leaves unanswered many interesting and intriguing questions, both at 

 the morphological and biochemical levels. This is the way of research. 

 In seeking an understanding of nature's mysteries, one is usually left 

 with more imponderables than one started with— which keeps the busi- 

 ness of research alive. In the field of male reproduction, despite the 

 efforts of numerous workers past and present, our understanding of the 



