126 



ANATOMY OF THE RABBIT 



directly associated with the degree of general speciaUzation of 

 the groups in which they occur. These organs have been designated 



A. 



B. 



Fig. 73. A. Plan of a single primitive kidney tubule in a 

 lower vertebrate, the cavity between the two layers of the 

 capsule and the cavity of the tubule represented in solid black: 

 gl, glomerulus; np, nephrostome; cl, coelomic epithelium; 

 d, longitudinal duct; t, main portion of tubule. 



B. S'cheme of the parts of the nephrons and their situa- 

 tions in the mammalian kidney, after Sperber: c, cortex; 

 iz, inner zone of the medulla; m, medulla; oz, outer zone of 

 the medulla; re, renal corpuscle; tc, convoluted portion of 

 proximal tubule; tk, thick segment of proximal tubule; tn, 

 thin segment of proximal tubule; ts, straight portion of 

 proximal tubule. The proximal tubules are unshaded, the 

 distal tubules grey, the collecting tubules black. 



as pronephros, mesonephros, and metanephros. The metanephros 

 is the aduh kidney in mammals, while the other two are embryonic 



