896 MR. W. WOODLAND ON THE [NoV. 27, 



It is also exceedingly probable that the completely median 

 position of the primitive posterior cardinals in the region of the 

 kidneys in mammals, is due to the absence of encroachment upon 

 the lumen of the veins by the kidneys. 



Recapitulation and Conclusion. 



To recapitulate the entire argument : In view of the fact that 

 the supply of arterial blood to the kidneys is only partial and 

 does not involve the whole aorta (the inference from this being 

 that a venous supply is unnecessary), and of the further facts that 

 the renal cardinal meshwoi'k is not found in those animals which 

 most requii'e it, and that in those animals in which it is found at 

 least half the blood avoids its passage ; seeing that when the 

 meshwork is absent there is no diminution in volume of the 

 kidney, and that the meshwork is radically different in regard to 

 its mode of origin as compared with the true portal system of the 

 liver ; seeing that the venous " portal capillaries " of the kidney 

 are too large to be pi'operly denoted by that term, and that, un- 

 like the hepatic-portal system, the walls of the kidney " capillaries " 

 contain no muscles and are devoid of a nervous supply, there is 

 every reason to believe on a priori grounds that the renal cardinal 

 mesliAvork is not excretory in nature. A posteriori evidence in 

 confirmation of this conclusion has also been supplied, as we have 

 seen, by the results of certain physiological experiments, some of 

 which, though not conducted in as satisfactory a manner as could 

 be wished from the present standpoint, yet were probably 

 suliiciently well performed to justify reference to them. 



If the renal cardinal meshwork is thus not excretoiy in nature, 

 then, it being extremely imjjrobable that the meshw^ork possesses 

 some other function, it follows that the association of the kidney 

 and vein is probably functionless. If functionless, it is on this 

 account certain that the meshwork is accidental in origin — a by- 

 product having no relation to the animal economy — and I have 

 supplied a certain amount of evidence to this effect. In short, I 

 have endeavoured to show that the renal cardinal meshwork is 

 simply an instance of the extension of a growing organ in the 

 direction of least resistance ; in other w^ords, a mechanical product 

 bearing no direct relation to the physiological needs of the animal. 



In conclusion I wish to express my indebtedness to Dr. Ridewood, 

 who very kindly read throiigh the manuscript and offered several 

 suggestions, and to Professor Starling, who kindly assisted me in 

 connection with the literature of the subject. 



Appendix. 



On the Production of Pelvic Veins; i. e., an additional sub-abdominal 

 communicatio7i bettceen the iliac and caudal veins and the 

 heart. 



Several reasons have been given in the paper referred to in the 

 text (10) to account foi' the return to the heart of the venous 



