1906.] '• REXAL-PORTAL SYSTEM." 887 



to tJae portal theoiy of the renal cardinal mesliwork — a veiy 

 necessary preliminary for the suggestions to follow. 



Theoretical Objections to the Portal Theory of the Renal 

 Carclin al Meshwork. 



Attributing a portal function to the renal cardinal meshwork 

 ordinarily implies that the kidney substance eliminates from the 

 venoits blood circulating through its sinuses a (nitrogenous) 

 product which is excretory* in nature. It also follows from 

 this supposition that those animals which have a " renal-portal 

 system " possess a considerable advantage over animals which 

 have not, since obviously in the former a far larger proportion of 

 the blood passes through the kidney (the " portal " kidney being 

 " supplied " from both an arterial and a venous source), and hence 

 there exist greater facilities for excretion. Assuming then the 

 hypothesis to be valid, we may reasonably expect to discover that 

 H " renal- portal system " exists in all those animals which manifest 

 the greatest activity, since, activity being coextensive with the 

 amount of excretory mattei- produced, they need it most. Orga,ns 

 in general are best' developed, i. e. most efficient in their mode of 

 function, in those animals where they are most required, and an 

 excretory renal-portal system being undeniably an improvement 

 on the non-portal kidney, this should conform to the general rule. 

 The expectation however is not justified by the facts : on the con- 

 trary, we find that in general the more active the animal the less 

 developed is the " renal-portal system " ! In the relatively inactive 

 cold-blooded Pisces, Amphibia and Reptilia, the " renal -portal 

 system" attains its maximum of development, whereas in the 

 active hot-blooded Aves and Mammalia it is either reduced or 

 absent. And this same irrelation between activity of the anim<d 

 and the presence of the renal cardinal meshwork can also he 

 observed in more special cases : e. g., the caudal vein forms a con- 

 spicuous renal meshwork in Pleuronectidse, but does not form one 

 at all in the Perch and Salmon ; indeed the degree to which the 

 renal cardinal meshwork is developed in Teleosts (and other groups) 

 is extremely variable. Thus, apart from other considerations to 

 be adduced, it follows solely from the general rule just mentioned 

 that the renal cardinal meshwork is probably not portal iu 

 function. 



Evidence of a more special character tends to the same conclusion. 

 The kidney, like all other organs, conforms to another general law, 

 viz., that size is proportional to work done. It is well known for 

 example that excision of one of the kidneys causes the companion 

 organ to enlarge considerably owing to the additional activity thus 

 deputed to it, and it is equally well known that the most active 

 animals possess the largest kidneys relatively to the size of the 



* The foUowina: arguments equall}- applj' on the supposition that the product is a 

 secretion (like that of the thyroid gland, e. g.) which is subsequently added to the 

 Wood. 



Proc. Zool. Soc— 1906, No. LIX. 59 



