890 MR. W. WOODLAND ON THE [Nov. 27, 



the portal blood contains a substance to ))e eliminated, and it does 

 not seek to escape a process of depuration so needful for tlie 

 maintenance of animal life. The same fact is illustrated elsewhere 

 in the vertebrate body, as e. g. in the gills of fishes and lungs of 

 Amniota. Now the present argument may best be presented in 

 the form of the following question : how is it, if the renal cardinal 

 meshwork be, as it is usually supposed to be, excretory in nature, 

 that a large pi-oportion of the venous blood returning from the 

 posterior portions of the body, nearly always adopts, in the case 

 of animals possessing a well-marked meshwork, an altei-native 

 direction of flow in returning to the heart, thus to a large extent 

 rendering the meshwork useless? If the renal cardinal mesh- 

 work exists for the purpose of purifying the venous blood, how is 

 it that in most cases half or more than half of the blood takes 

 the opportunity of evading the process*. To realise this fact 

 (wholly unexplainable on the portal theory) it is only necessary 

 to call to mind the large epigastric veins of Amphibia and 

 Reptilia and the coccygeo-mesenteric of Birds, which evidently 

 carry back to the heart a very considerable portion of the venous 

 blood from the posterior parts of the body, which otherwise would 

 be compelled to traverse the kidney substance. The same 

 phenomenon is observable in most Teleosts, where usually one 

 posterior cardinal alone (the left) is involved in the formation of 

 the renal cardinal meshwork, and where in every such case this 

 cardinal " shows a tendency to become reduced " (Wiedersheim), 

 the greater portion of the blood passing direct to the heart 

 through the swollen and medianly situated posteiior cai'dinal 

 whose lumen is not obstructed. Again, " in a few osseous fishes, 

 as the Shad, some of the caudal branches of the vertebral system 

 of veins anastomose toith the veins of the rectum, and thus form 

 part of the roots of the portal system " (Owen) ; these anastomoses 

 ''representing a commencement of the anterior abdominal or 

 epigastric vein of higher types " (Balfour). 



Finally, it may be urged as an objection of some importance, 

 that the renal cardinal meshwork diflfers from a capillarisation such 

 that of the true portal system of the liver in the facts that the 

 walls of the larger veins forming the renal meshwork possess no 

 muscular tissue t and are not supplied with vaso-motor nerves, 

 the larger branches of the portal vein, on the other hand, being 



* I maj' here add yet another objection to the supposition tliat the renal cardinal 

 meshwork is portal in function, and this is that the needlessness of such an 

 additional supply of venous blood to the kidneys in the Ichthyopsida and Sauropsida 

 is sufficiently demonstrated by the fact that only a portion of the blood in the 

 dorsal aorta itself enters the kidney substance and not the whole. The possible 

 reply that the whole of the dorsal aorta could not ramify through the kidney 

 because such a capillarisation would destroy the forcible flow of blood to the hind- 

 limbs and tail, may be met by the fact that the blood propelled from the heart does 

 in all fishes first traverse the capillaries of the gill-filaments before entering the 

 dorsal aorta to supply the locomotor tail, and what is possible in the case of the 

 tail of fishes is possible for the hind-limbs and tails of animals (certainly in 

 Amphibia, Reptilia, and Aves) possessing a renal meshwork. 



t Each kidney tubule being alone invested by an " accurately-fitting layer of the 

 flattened epithelial lining of the vein" (Shore, 6). 



