364 



which Woodland Id a foot note is willing to admit with regard to 

 the myocardium and kidney, but surely this only shews that homologous 

 structures need not have analogous functions. 



It is urged as a fourth objection that the whole of the blood 

 coming from the hepatic portal vein passes through the liver, while, 

 with the renal portal there co-rexists the epigastric veins of Amphibia 

 and Reptiles and the coccygeo-mesenteric of Birds, and the argument 

 is presented in the form of a question. "How is it" asks Woodland 

 "if the renal cardinal meshwork be, as it is usually supposed to be, 

 excretory in nature that a large proportion of the venous blood re- 

 turning from the posterior portion of the body, nearly always adopts 

 in the case of animals possessing a well-marked meshwork, an alter- 

 native direction of flow in returning to the heart, thus to a large ex- 

 tent rendering the meshwork useless?" We are not concerned here 

 with the evolution of the vascular system, and in reply to the above 

 quoted question it need only be said that the mere fact that the whole 

 of the blood from the lower limbs does not return through the kidney 

 is no argument against the portal significance of that which does. 



There is now one further theoretical point which I consider has 

 direct bearing on this question. Whether different in origin or not, 

 there is a strong anatomical resemblance between the two sinusoidal 

 systems in the mesonephros and the kidney. Although maintaining a 

 difterence of origin, Shore (20) says: "The same sinus-like character 

 of the vascular network of the adult vertebrate liver was pointed out 

 by Lewis, Jones and myself (21), for we found in no case any base- 

 ment membrane between the liver cells and the blood channels, and in 

 several instances, e. g. eel, frog, newt, tortoise, chick etc., we found 

 that the blood spaces have the same sinus -like character as in the 

 mesonephros of the frog, and that the flattened epithelial walls of the 

 sinuses are closely adapted to the irregular surfaces of the tubules 

 around them". Then again Minot (12) shewed the sinusoidal nature 

 of the circulation in the amphibian mesonephros. In 1900 he called 

 attention to the differences between a sinusoid and a true capillary, 

 of which, the close fitting of the former with "no or exceedingly little 

 connective tissue" between it and the cells of the organ, is important 

 in this connection as it points to a functional relation between the 

 blood and the organ. In the same paper the presence of sinusoids in 

 the liver was also demonstrated. This occurrence of sinusoids in liver 

 and mesonephros was again maintained four years later by Lewis (11). 

 Such a striking resemblance in anatomical relationship, bringing, as it 

 does, the blood into similar close approximation with the active se- 



