302 THE ELASMOBRANCH FISHES 



ducts. Several of the anterior segmental ducts may now become vasa efferentia, 

 but others which are on the mesorchium may fail to reach the tissue of the 

 testis. Those actually penetrating each testis in Squatina (v.e., fig. 254a) are 

 six in number. In Squalus four such enter, while four others end on the mes- 

 orchium. In Scyllium two or three vasa efferentia are present and in the rays 

 (fig. 254b) a single vas efferens is present. In this form the vas efferens joins 

 the vas deferens directly without the intermediation of a longitudinal canal. 



The passageway for the sex cells of the adult male, then, is from the testes 

 through the vasa efferentia into the greatly coiled Wolffian ducts each of which 

 is now a vas deferens. We may next notice in detail the changes which the 

 Wolffian duct and its associated parts undergo in its metamorphosis into the 

 vas deferens. We shall first consider the changes undergone in the anterior 

 segment of the kidney. 



The anterior part of the kidney, which in the young male is in the service 

 of the urinary system, undergoes profound modification in the adult male, 

 characteristically coming to be of large size (Borcea, 1906). If a transverse 

 section is taken of this area in the adult it will be found to be devoid of the 

 Bowman's capsules which were previously present in it (see fig. 255b, Acan- 

 thias) . In their places will be found numerous enlarged sacs the walls of which 

 have become greatly thickened. The two types of cells which compose the walls 

 are: (1) ciliated cells (ciZ., fig. 255b), which border on the lumen, and (2) non- 

 ciliated cells with basal nuclei. These cells secrete a viscous whitish substance 

 which acts as a seminal fluid. The upper end of the kidney, therefore, which at 

 first functioned in the young male in the removal of the nitrogenous waste, 

 has thus entirely changed its function in the adult so that it now acts as a 

 gland for the secreting of a kind of spermatic fluid. 



Upon the transformation of the anterior part of the kidney, the vas deferens 

 becomes a coiled tube {Squalus, fig. 253b; Raja, fig. 254b; Torpedo) which as 

 it passes posteriorly receives collecting tubules. In the region of the posterior 

 kidney it becomes the enlarged vesicula seminalis into which no collecting 

 tubules empty. The vesicula Seminalis in many of the sharks (Squalus, fig. 

 253b, v.s.) is a long tube but in the rays (fig. 254b) it is much shorter. 



When opened longitudinally the vesicula seminalis in Squalus shows a 

 series of transverse semipartitions which give to the inner wall a corrugated 

 appearance. Along this wall in the breeding season are found myriads of 

 sperm cells or spermatozoa. 



The seminal vesicles of the right and left side empty into the enlarged 

 urogenital sinus (u.s., fig. 253b) usually ventral to and laterad of the entrance 

 of the ureter (u.). Passing forward on each side of the urinary sinus is the 

 blind sperm sac (sc.) which appears to be an evagination of the urinary sinus 

 but which is formed from the posterior remnants of an oviduct like that of the 

 female. The sperm sac of Squalus or of Raja is of small size and in the rays it 

 has been spoken of as a urinary bladder. In Squatina (fig. 254a) and Scyllium 

 (see p. 189, fig. 177a) the sacs reach a much greater length. Since the sinus 

 receives both the nitrogenous waste and spermatozoa it is properly designated 



