THE URINARY ORGANS. 209 



observed ; but what we do know from the labours of Rathke, 

 J. Miiller, Valentin, and Bischoff, with respect to its subse- 

 quent conditions, perfectly accords with the statements of 

 Kemak, except that, in this case, the glandular canals appear to 

 be developed upon the type of the salivary glands, and are not 

 hollow from the commencement. The rudimentary kidneys, in 

 the Mammalia, at first, present nothing but the pelvis and a 

 certain number of clavate hollow protrusions continuous with it 

 — the calices. From each of the latter is subsequently formed, 

 by continued budding, a bundle of tubuli uriniferi, each of 

 which bundles ultimately constitutes a Malpighian pyramid 

 and the cortical substance appertaining to it; whilst, at the 

 same time, the kidney expands into a corresponding number 

 of lobes. The tubuli uriniferi are at first solid, composed 

 solely of cells and without any membrana propria. In the 

 course of development the latter arises, probably from a plasma 

 afforded by the cells, and the cavity of the canal is formed, in 

 consequence, it may be supposed, of the collection of a fluid 

 between the cells ; simultaneously with which the tubules begin 

 to grow rapidly in length, and to become convoluted. The 

 Malpighian bodies are originally nothing more than solid, 

 clavate, thickened extremities of the rudimentary tubuli urini- 

 feri. The interior cells of these pyriform or rounded bodies, 

 subsequently become capillaries, which are continuous, at two 

 points, with the vessels outside, whilst the most exterior form 

 the epithelium , which joins that of the tubulus uriniferus and, 

 like it, is invested with a membrana propria, which is of course 

 deficient where the afferent and efferent vessels enter and 

 emerge, at which point it may be said to be perforated. In the 

 newborn child, according to Harting, the renal canals are three 

 times more slender than in the adult, whence, as the kidney 

 of the latter is only twice the size of that of the child, it is 

 obvious that, at any rate after birth, no tubules are formed. 



With respect to the physiological relations, I would merely 

 offer the following remarks. There can be no question that 

 the peculiar vascular conditions in the kidney, in accordance 

 with which the blood circulates in special coils projecting into 

 the commencement of the tubuli uriniferi, before it passes into the 

 proper capillary plexus of the organ, are most intimately con- 

 nected with the secretion of a large proportion of water in the 



ii. 14 



