361 



Part III. 



Some remarks on the significance of the renal portal 



System. 



Woodland (23) in his paper entitled "A Suggestion concerning 

 the Origin and Significance of the 'Renal Portal System'" has pro- 

 posed to replace the terms "Renal portal system" and "Renal portal 

 vein" by "Rena{ cardinal meshwork" and "Post renal vein". In the 

 course of my examination of the three specimens described in the 

 preceding pages, I noticed that the size of the kidneys varied in a 

 way that seemed contrary to what might be expected, if Woodland's 

 theory of the non-portal nature of the kidney circulation be the correct 

 one; and so was led to consider critically his arguments. The result 

 of these enquiries has been that I think the weight of evidence is 

 against such a view, and that the circulation in the kidney is truly 

 portal. The question may be conveniently regarded from two points 

 of view, the morphological and the physiological. 



Morphological considerations. 



I propose, in the first place, to consider the arguments adduced 

 in the paper cited above; this I am able to do the more easily since 

 they are so lucidly brought forward. The chief theoretical objections 

 to regarding the renal portal system as a portal system are, according 

 to Woodland, four in number and I shall consider these in order. 

 The first is, that if the circulation be a portal one, them those animals 

 which possess it have an advantage in excretion over others which 

 do not. 



It might therefore be expected that the most active animals, which 

 require to get rid of most excretory matter, would have the best de- 

 veloped portal system; and the argument is summed up by the following 



sentence " in general we find the more active the animal 



the less developed is the renal portal system"! As examples, on 

 the one hand, are given Pisces, Amphibia and Reptiles, and on the 

 other Aves ^^and Mammalia. It is here assumed that a mesonephros 

 supplied by a portal system (at any rate in Pisces and Amphibia) is 

 a more efficient means of excretion than a metanephros not so supplied ; 

 whereas as a rule in the animal kingdom, when one organ is replaced 

 or modified in the higher groups, it is because of the greater efficiency 

 thereby obtained ^). There any many factors which contribute to the 



1) Two conditioDS are given by Papin (15) which "determine the 

 disappearance of the renal portal system in the mammals". They are 1) 



