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



evident that the " portal " kidney will resemble in all respects 

 the kidney of Mammalia, and the kidney of the Yertebrata 

 generally will thns be proved, to be identical in structure and 

 function throughout *. Finally, Prof. Stai-ling informs me that 

 it has been experimentally proved that ligature of the post- renal 

 and dorso-lumbar veins in a living animal does not interfei^e 

 appreciably with the normal excretion of the kidneys t — which 

 fact I think by itself sufficiently confirms the conclusion 1 had 

 previously arrived at on theoretical grounds. 



The Nature of the Renal Cardinal Meshwork. 



Accepting then as valid, as I think we must do, the conclusion 

 that the renal cardinal meshwork is not excretory in nature, it is 

 evident that the question as to the origin and significance of this 

 structure still remains to be ansAvered. What, then, is a possible 

 cause of the formation of the renal meshwork in the vast majority 

 of the lower vertebrata ? 



It must first be i^emarked as a most significant fact that the 

 successively posterior developments of the kidney in the phylogeny 

 and ontogeny of vertebrates (the pronephros, mesonephi-os, and 

 metanephros) follow the path of the veins of the body posteriorly- — 

 the kidney elements select the actual path of the veins as a site 

 for their development. Thus the pronephiic tubules form a renal 

 cardinal meshwork in connection with the anterior portions of the 

 posterior cardinal veins, and are in consequence situated some 

 distance from the median line ; the mesonephroi, with the 

 posterior cardinals, approach the median line of the animal the 

 more posteriorly they are situated, and the metanephroi (except 

 in mammals) are similarly placed still more in apposition with the 

 vertebral column, since they are still nearer the junction of the 

 posterior cardinals to form the caudal vein. Thus it cannot be 

 doubted but that the kidney develops in most cases in connection 

 with the vein as if for a purpose, but since we cannot assume 

 that the position of an organ in the body is determined by the 

 desirability of that position^ — a teleological mode of argument too 

 often employed — we must believe that the coelomic epithelium 

 (or the kidney-forming substance above it) has, in the vicinity of 



8qualida3 examined by M.Vialleton are, as he says, " fort irregulieres, elles presenteiit 

 <les dilatations considerables alternant avec des r^trecissements marques, et des 

 bosselures laterales terminees en cnl-de-sac. Leurs parois, d'une minceur extreme, 

 )ie possedent pas de fibres musculaires de sorte que, suv les coupes, on dirait do 

 simples lacunes creusees dans le tissu conjunctif, etlimitees par nn endothelium . . ." 

 He further states that there are two sets of " capillaries " in the hidney suhstance, 

 one of which consists of very small vessels which soon enter into the second set 

 ivhich, on the other hand, consists of the system of largely developed sinusoids 

 connecting .Jacobson's veins with the interrenal — the renal cardinal meshwork. 

 I think this statement by an impartial observer converts my "very probable 

 supposition " into a certainty. 



* See footnote on p. 895. 



f See Gurwitsch, Pfiiiger's Arcliiv, vol. xei. p, 71 et seq., 1902. Prof. Starling- 

 says that the diminution in excretion of urine obtained by Gurwitsch is to be 

 regarded as due to the conditions of the operation merely. 



