b BINAR LONNBEEG, ANATOMICAL NOTES ON EAST AERICAN MAMMALS. 



With regard to the aquatic animals another explanation might be tried. It is 

 clear that such animals which exclusively, or at least chiefly, obtain their food from 

 the water, and often even may swallow it below the surface, are apt to get a con- 

 siderable quantity of water into the alimentary canal, and certainly more than is 

 needed for the digestion. This surplus of water must be removed so that it shall 

 not hamper the digestion, and this must at least chiefly take place by absorption 

 into the circulatory system and secretion through the kidneys. It appears thus as 

 if the latter organs of such an aquatic animal should be obliged to secern compara- 

 tively more fluid than those of a strictly terrestrial mammal. If this should be the 

 cause of the development of lobulated kidneys, the presence of such in Bovince might be 

 explained as an inheritance from the ancestors which might have aquired that character- 

 istic at the same period as they lost the peripheric colic coil, as is mentioned above.' 



It must, however, be admitted that it is difficult to conceive that such an 

 increased activity required from the kidneys of aquatic animals should in any way 

 be facilitated by the lobulation of these organs. The secretive power of the kidneys 

 depends, of course, upon the condition and quality of the secerning epithelium, and 

 this can hardly be influenced by the lobulation, as it seems. 



Against the connection between aquatic habits and lobulation of the kidneys 

 speaks also, as it will appear at first, the fact that these organs are not lobulated 

 in the now living Sirenia in spite of their partaking of their food below the surface 

 of the water. In his valuable manual^ »Die Saugetiere» Weber says (1. c, p. 737) 

 about this: »Die Nieren sind bei Halicore glatt, bei Manatus oberflachlich gelappt, 

 aber niemals in Renculi verteilt wie bei Cetaceen. » In a foetus of Trichechus inunguis 

 which I have examined, the kidneys were comparatively very large, but had a smooth 

 surface. Quite recently Riha^ has described the kidneys of Halicore, and proved 

 that it has a peculiar structure with the urether dividing in two longitudinal branches 

 running from the hilus in either direction. — It is this which Owen has termed »a 

 single pelvis* into which » several lateral ridges* extend. — The cortical substance 

 of these kidneys form an exteriorly smooth and continuous layer, but the medullary 

 substance is divided by — to quote Riha — »senkrecht auf die Nierenachse ste- 

 henden, bindegewebigen Quersepten, welche sich erst in der Rindensubstanz auflosen, 

 Auf diese Weise ragen die Pyramiden mit freier Papille und freier Seitenwand in den 

 Nierengang». This interior subdivision by septa of connective tissue proves that the 

 kidney of Halicore really is not such a simple organ as it looks superficially. It 

 might be assumed that it originally has been a lobulated kidney which secondarily 

 has become more compact by partial fusion of the renculi, but from a physiological 

 point of view it appears to be almost equivalent to a lobulated kidney. There is a 

 fact which speaks rather strongly for the assumption that the kidney of the Sirenia 



^ It needs perhaps to be emphasized that I do not mean by this that the ancestors of Bovince were real 

 water-animals, far from that, but they may have lived to great extent in and at swamps and found their food 

 chiefly in such places. 



^ Jena 1904. 



8 Zeitschr. f. Morpli. u. Anthropol. Bd. XIII. Hft. 3. 



