54 MK. SWALE VINCENT ON THE 



The interrenal is generally much thicker behind than in front (PI. IX. figs. 1, 3, 

 & 4) ; in fact, while it is posteriorly often markedly bulbous, it usually tapers oif 

 anteriorly into a broken line of extreme tenuity. It diminishes in diameter, however, 

 not regularly, but is often more or less moniliform ; the constrictions may be 

 complete here and there, and at the anterior extremity one often finds several small 

 pieces of interrenal separated by a considerable interval from the rest of the body 

 (PI. IX. figs. 1, 3, & 4 ; PI. X. figs. 5 & 7, a.i.r.). 



In the Batoidei the interrenal is never quite symmetrical ; nearly always the body of 

 one side extends further forward than that of the other, and in one case, in Raja batis 

 (PL X. fig. 6, i.r.), I found a complete and comparatively thick bridge connecting the 

 interrenal of one side with that of the other. This might perhaps be looked upon as 

 a single body behind, which became divided in front ; in this instance the organ 

 extended further forward on the right side, and further backward on the left. 



In some cases (e. g., Acanthias) the unpaired interrenal body appears to be placed 

 not quite mesially, but is laid on the median surface of one or other kidney (PI. X. 

 fig. 5, i.r.). 



Occasionally {Raja maculata) the anterior piece of the interrenal of each side, which 

 is cut ofl' by more or less of an interval from the rest of the body, shows curious claw- 

 like processes on its outer side running in the kidney-substance towards the ureter 

 (PI. X. fig. 7, a.i.r.). 



Balfour quotes Semper as describing an anatomical connection between the inter- 

 renal and the paired bodies. Balfour questions this, and I am convinced from the 

 examination of several fresh specimens, both of ScyUiwn and Raja, that there is never 

 any such connection or continuity. The tivo kinds of structure are aliuays totally 

 independent and unconnected. I have mentioned in the historical section Balfour's 

 surmises with regard to the existence of a third kind of body in relation to the kidney 

 in Scyllium, and I have intimated that masses of adenoid tissue were to be expected, 

 and were frequently found in various situations in and about the kidney. I have, 

 nevertheless, carefully searched for anything which might rank as a " third kind of 

 body." I have been able to examine a number of fair-sized perfectly fresh specimens, 

 and I have failed entirely to find anything of the kind. So that we may consider that 

 we have to limit the morphological and physiological problem, difficult as it is, to the 

 relationships and significance of the paired segmental bodies and the " ochre-yellow 

 strips " or interrenal bodies. The problem which naturally presents itself is : — Which 

 of these two structures (if not both) corresponds to the suprarenal capsules of Teleosts 

 and higher Vertebrates 1 For an account of the discussion see the historical section 

 above. My own view will be stated after I have given a description of the histology. 



In the above account I have treated the Sharks and Rays together, because there is 

 not sufficient difference between the general arrangement in the two cases to make a 

 separate description necessary. 



