432 DISCOVERY REPORTS 



two major veins accompanied by smaller ones. The renal veins on the left side enter the 

 left member of the pair of post-cavae at the point where it turns towards the middle line 

 and crosses the aorta. On the right side the renal veins enter the common post-caval 

 trunk where it turns forward before penetrating the diaphragm. 



It is thus seen that the arteries enter and the veins leave the kidney at the anterior end 

 of the organ and the ureter leaves at the posterior end. Thus the single hilus, which 

 admits both the blood vessels and the ureter in non-lobulated kidneys, has become 

 dissociated in the Cetacean kidney. Anthony (1922) traces this process of dissociation 

 of the hilus from the condition found in the otter, which has a lobulated kidney and in 

 which the ureter leaves from the ventral face of the organ, up to the condition found in 

 the Cetacea, where the ureter leaves the kidney at its posterior end. In the Otariidae, the 

 eared seals, the kidney is only superficially divided and the renal arteries run along the 

 border of the kidney before entering it, while the veins leave from the middle of the 

 mesal border — which is concave. These seals thus have a completely undivided hilus, 

 the ureter leaving from the mesal face. In their general anatomy these seals are the least 

 modified for aquatic life. In Lobodon carcinophaga and Ommatophoca rossi, which are 

 the most modified for aquatic life, the hilus is tending to be dissociated. The ureter has 

 migrated on to the ventral face of the kidney. In the Cetacea such as Mesoplodon and 

 Ziphias the ureter emerges about half-way along the ventral face of the kidney, while in 

 Mystacocetes the dissociation of the hilus is quite complete and the ureter leaves the 

 kidney at its extreme posterior end. 



It seems quite evident that the degree of fission of the hilus is a function of the degree 

 of lobulation of the kidney, since the hilus is most dissociated in those forms, such as 

 Balaenoptera, where the kidney is very finely divided into numerous lobules, and least 

 dissociated in forms such as the Otariidae where the kidney is only superficially divided. 

 Daudt, as will be mentioned again later, laid great stress on a small backwardly directed 

 branch of the ureter found in Balaenoptera at the extreme posterior end of the kidney 

 (Fig. 26 e 2 ) and in Phocaena phocaena at about one-third of the length of the organ from 

 its posterior end. Daudt considered that this backwardly directed branch represents 

 the posterior calix major of the kidneys of other mammals, and that the main urinary 

 duct of the kidney represents the anterior calix major. If this is correct then the true 

 hilus of the kidney lies at the junction of these two calices. Actually the whole mesal 

 slit, which is open throughout its length in the foetus, must be looked upon as a greatly 

 elongated hilus, extending from the entrance of the blood vessels at the anterior end of 

 the kidney to the posterior end where the two calices join. Thus the Cetacean kidney 

 is derived from that of the ordinary mammalian pattern by extreme elongation of the 

 anterior calix along an antero-posterior line. 



The adrenal bodies (Fig. 22 i) are a pair of flat bean-shaped organs (in the adult they 

 are almost circular) lying immediately in front of the renal veins on each side. They 

 receive adrenal arteries mesally and slightly posteriorly. Similarly adrenal veins leave 

 them in the same positions and run to the postcavae slightly anterior to the adrenal 

 arteries. 



