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



region. The results showed that levels of 17a-hydroxylase and aroma- 

 tase as well as P-450 concentration increased as the glandular tissue 

 developed. As yet the functional significance of estrogen production by 

 Necturus testis has not been investigated. 



INTRODUCTION 



Urodele amphibians of the genus Necturus are widely distributed 

 throughout the eastern and middle regions of North America, where 

 they are extremely abundant in rivers tributary to the Great Lakes and 

 to inland streams and small lakes. The ability to survive in waters of 

 such diverse characteristics apparently accounts for their wide distri- 

 bution. Necturus, one of the largest of salamanders, is primarily noctur- 

 nal, although in very muddy or reedy habitats it may be more or less 

 active during the day, and is preeminently aquatic. These salamanders 

 are also usually active throughout the whole year and do not, it seems, 

 undergo periods of true hibernation. 



The sexes of Necturus are similar in both form and coloration. Fol- 

 lowing a primitive courtship behavior the animals mate, depending on 

 their regional distribution, throughout the summer and fall. Fertiliza- 

 tion is internal by means of spermatophores produced by the males. The 

 male vent is larger than that of the female, becomes inflamed during the 

 breeding season, and is capable of eversion to expose two papillae that 

 possibly aid in the deposition of spermatophores into the cloaca of the 

 female. Cloacal glands occur in the male and are presumably involved 

 in the formation of spermatophores. The spermatozoa are stored over 

 the winter months in spermathecae of the females, which then undergo a 

 short spawning season in the following spring and deposit eggs in rudi- 

 mentary nests that can be guarded by either parent. 



MORPHOLOGY OF NECTURUS TESTIS 



As in all amphibia, the paired elongate testes of Necturus are 

 abdominal in position, bordering the kidneys and attached to the dorsal 

 body wall by a mesorchium (Fig. 1). Within this mesenteric membrane 

 lies the vascular system of the testis and vasa efferentia, which convey 

 the spermatozoa to the Wolffian ducts — long, coiled structures in 

 which spermatozoa are stored prior to encapsulation within the spermat- 

 ophores. 



The structural unit of Necturus testes is the cyst which contains the 

 germ cells and associated somatic cells, analogous to Sertoli cells found 

 in amniote testes. These units are enclosed and contained in larger struc- 

 tures, the seminiferous lobules. Surrounding the lobules is the interlobu- 

 lar tissue in which is found the Leydig cells. The organization of the 

 testis consists of seminiferous lobules radiating outward to the periphery 



