438 Bashford Dean Memorial Volume 



In the absence of any statements to the contrary, it may be assumed that the "kidney'" 

 of Hawkes' specimen was a paired structure, and that the two, more or less separate, 

 members were of equal length. As already noted, in one of my specimens (and less 

 significantly in CoUett's large specimen) the left mesonephros is shorter than the right. 

 This does not necessarily mean a decrease in function of the left mesonephros, since 

 a shortening of the thin anterior end might readily be compensated by a hardly noticeable 

 increase in thickness posteriorly. A concentration of the adult female mesonephros into 

 a compact organ situated in the posterior part of the body cavity is characteristic of the 

 highly specialized elasmobranchs. 



Concerning the mesonephroi of the female Heptanchus, Daniel (1934, p. 287) writes 

 as follows: ''Each kidney extends as a narrow ribbon of tissue from the pericardio- 

 peritoneal septum posteriorly one-half the length of the body cavity; back of this it 

 broadens out and becomes much thicker so that the main mass of the tissue lies posterior 

 to the region of the superior mesenteric artery." From an inspection of Daniel's figures 

 it appears that the broadening of the posterior part of the "kidney" is rather abrupt, not 

 gradual as in the case of Chlaynydoselachus. The assertion that the kidney of the female 

 Heptanchus extends from the pericardio-peritoneal septum is hardly understandable in 

 view of DaniePs statement (p. 289) that the kidney of the male extends farther forward 

 than that of the female. 



The Urinary Sinuses. — In specimen No. IV, which is immature, a probe inserted 

 through the urethral orifice passes in one direction (anterodorsally) only, for a distance 

 of about 10 mm. The slender cavity thus explored is the rudimentary left urinary sinus. 

 Its posterior half is imbedded in the thick dorsal wall of the urogenital sinus, while its 

 anterior half lies in a thick portion of the dorsal mesentery supporting the two uteri 

 which are joined by their medial walls for a distance of 50 mm. anterior to the urogenital 

 sinus. The left mesonephric duct, too small to be probed but clearly visible with a hand 

 lens, extends anteriorly from the left urinary sinus along the base of the dorsal mesentery 

 close to the left mesonephros. There is a right urinary sinus, of the same size as the left 

 and in a corresponding position. Anteriorly, it is continuous with the right mesonephric 

 duct which lies alongside the left; but I could not find any opening from the right urinary 

 sinus into the urogenital sinus, either by way of the urethral orifice which serves as an 

 outlet for the left mesonephric duct, or otherwise. The right urinary sinus was found 

 by dissection, using the right mesonephric duct as a guide. I could not find any aperture 

 connecting the two urinary sinuses, which are separated by a thick septum. 



In specimen No. Ill the two urinary sinuses (Text-figure 91a), right and left, lie 

 close to the median plane. The left urinary sinus extends 75 mm. anterior to the urethral 

 orifice. Near its posterior end this sinus is broad but shallow; its greatest width is 

 9 mm. For a distance of 25 mm. from the urethral orifice, the expanded posterior portion 

 of the left urinary sinus lies within the dorsal and left lateral wall of the urogenital sinus. 

 Here, only the medial border of the left urinary sinus comes into relation with the dorsal 

 mesentery which connects the urogenital sinus with the dorsal body wall and with the 



