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



cells are not actually present in the interlobular tissue but occur as a 

 component of the boundary wall surrounding the seminiferous lobules. 

 This concept of Leydig cell development was originated by Marshall 

 and Lofts (1956) who suggested, from investigations restricted to light 

 microscopic observations of frozen sections colored with a Sudan dye, 

 that in the teleost testis a lobular boundary cell was the homologue of 

 the Leydig cell present in the testis of these amniotes. This initial observ- 

 ation eventually became expanded to include the urodele amphibia 

 where it has been routinely reported that lobular boundary, perilobular, 

 or pericystic cells were analogous, if not homologous, to Leydig cells of 

 the amniote testis (see review by Lofts 1968; Roosen-Runge 1977; Pils- 

 worth and Setchell 1981). This concept, however, became confused 

 when, from various descriptions of the teleost testis using the more criti- 

 cal resolving power of the electron microscope, it was reported that the 

 lobular boundary cell actually corresponds to the Sertoli cell (see review 

 by Grier 1981). The situation is further complicated in that anamniotes 

 undergo a seasonal cycle of testicular activity, and so, depending upon 

 the stage of spermatogenesis, Leydig cells may or may not appear con- 

 spicuous. This becomes an important point if the observations being 

 carried out use the light microscope for examination of testis sections, 

 since the resolution of this instrument often precludes the positive loca- 

 tion and identity of Leydig cells. An attempt to clarify the question 

 concerning the presence and identity of Leydig cells in anamniotes has 

 recently been carried out by Grier (1981). 



Grier (1981) re-evaluated the literature pertaining to the structure 

 of the teleost testis and concluded that the term lobular boundary cell 

 was no longer tenable as the definition of Leydig cells in these anamni- 

 otes. In fact, in this vertebrate group the description of the lobular 

 boundary cells as Leydig cells is erroneous. From its location, and other 

 morphological criteria, the lobular boundary cell actually represents the 

 Sertoli cell of the teleost testis. In view of this, Grier strongly stated that 

 the term lobular boundary cell used to describe Leydig cells in the tele- 

 ost testis be discontinued. In our studies on Necturus testis we have 

 reached a similar conclusion. First, Leydig cells at various stages of dif- 

 ferentiation appear to be a constant component of Necturus testis 

 throughout the year. Secondly, these Leydig cells are present in the 

 interlobular compartment arising from precursor cells that are a per- 

 manent feature of this tissue. Thus, the concept of the lobular boundary 

 cell is also no longer applicable in the species that we have investigated. 

 Furthermore, the presence of myoid cells in the interlobular tissue of N. 

 maculosus testis, which often excluded the Leydig cells from direct con- 

 tact with the seminiferous lobules, is morphologically reminiscent of the 

 anatomical arrangement present in the amniote testis. It would seem, 

 therefore, that the organization of the testis in Necturus, and possibly in 



