Tlio (Icvelüpinent of llie kidney in t.lie rabbit. 



297 



/ 



ruliis has grown in size, the blood cavities have changed into capillaries, 

 while the cells covering it have lost their cubical character, and are 

 arranged around it as a squamous epithelium: it communicates on one 

 side by a narrow neck lined by short cubical 

 cells with its convoluted tube. 



It will be seen that the belief that the 

 Bowman's capsule is caused by the invagina- 

 tion by the glomerulus of the succular end 

 of the tubule is incorrect. The capsule is 

 from the first a spoonbowl with hollow sides, 

 and is moulded on the bend of its tubule; 

 it is fairly fully formed before the glomerulus 

 appears at all. 



Approaches to the Adult Condition. 



Later stages of the development shew 

 close approximation to the adult form. In 

 an embryo of 26 or 28 days the primary 

 renal vesicles are still seen, but a zone not 

 recognisable in younger embryos has formed 

 midway between the cortex and the medulla, 

 where the convoluted tubules which join the 

 arms of Henle's loop assume a corkscrew 

 shape as they pass into the loop and these 

 cork-shaped spiral tubules come to occupy a 

 very definite zone intermediate between cortex 

 and medulla. 



In Fig. 13 the adult renal tubule is re- 

 presented, and in Fig. 14 a section of the 

 whole adult Kidney is given. It will be seen 

 that in the cortical zone A. there are con- 

 voluted tubules and Malpighian bodies. In 

 the zone B and C^) we find the spillai thick 



D 



u 



An adult tubule is repre- 

 sented lying in the zones 

 A, B, C, D and E. 



^) In the Adult Kidney as I hope to shew in a subsequent paper the zones 

 B and C differ from each other both histologically and physiologically. 



