PLATANISTA. 471 



under an aquatic life. According to our present knowledge, the only explanation to 

 offer for the diminutive and modified character of this eye is on the theory of disuse 

 arising from the absence of conditions favourable to vision ; and to this may probably 

 be added the action, to a limited degree, of natural selection. 



There are difficulties, however, even in such an explanation, because there is not 

 such a wide difference between the conditions of the Grangetic Platanist and those of 

 the Irawady dolphin, or in anything connected with their respective river-systems as 

 to easily account for the great degradation of the organ of vision in the one case, and 

 the quite ordinarily sized eye in the other, as well developed as that of any marine 

 Cetacean. 



Urinary organs. — The kidney is a flattened, cake-like gland ; in the adult 4 

 inches long by 3*50 inches in extreme breadth. The anterior end is rather pointed and 

 turned towards the internal border. The posterior surface is made up of forty-seven, 

 more or less, hexagonal lobules, flat, or slightly convex externally and packed closely 

 together by their opposed faces. Laterally and internally, a few of the lobules become 

 fused together. Nineteen of the marginal lobules of the dorsal surface are common 

 to the two faces of the organ, while there are twenty-nine to thirty besides these 

 visible on the anterior aspect, so that the kidney is made up of about eight lobules, 

 visible externally. They vary from half an inch to one inch in superficial area, but 

 are destitute of conical apices. 



The cortical layer occupies the greater part of the lobules ; some of the papillae 

 have as many as two or three mammilliform processes. 



There are generally three calyces opening into a common dilatation (pelvis of 

 lobule) of the duct at the base of the united lobules. In these cases generally one 

 of the papiflse has its apex directed towards the periphery of the kidney. 



Ureter. — The pelvis of the ureter is formed by the junction of six branches 

 resulting from the union of the secondary and tertiary ducts of the renal lobules. 

 The ureter altogether is 6 inches long. In the male, after leaving the kidney, it 

 crosses behind the lower external corner of the testicle and beyond that point it 

 passes behind a considerable portion of the abdominal venous plexus, which rests 

 on it, and immediately below this it is posterior to the transverse coil of the vas 

 deferens, and then a little further backwards and inwards it crosses over the descend- 

 ing coil of the generative duct to the bladder. It preserves the same general direc- 

 tion in the female, running downwards to the anterior wall of the vagina tiU on a 

 level with the first great transverse fold of that channel. In the first part of its 

 course it lies close behind the origin of the ovary. 



The renal artery and vein enter the kidney at the upper extremity of the longi-. 

 tudinal groove. The artery is internal and dorsal to the vein. It is first placed in 

 a deep sulcus, and the main trunk runs along the internal margin of the groove by 

 the side of the branches of the ureter, and divides into numerous twigs, which reach 

 the substance of the kidney by passing behind the ureter. The vein leaves the 

 kidney external and anterior to the artery and lies along the outer margin of the 

 groove. 



