THE MESONEPHROS 



195 



the uephrostoiiie. After leaving the region of the renal eorpnsele, the 

 tubule continues as a larger proximal convoluted portion. This 

 convoluted ])ortion formed by low eohnnnar cells with a brush l)()r- 

 der then joins a short constricted region of the tubule com]K)sed of 

 ciliated cuboidai cells. Passing from the constricted portion, the 

 tubule again becomes wider and convoluted, forming the distal 

 convoluted ])ortion which is comi)osed of cuboidai cells often show- 

 ing cytoplasmic striations, and fuses with a short, straight, con- 

 necting ])iece that em])ties with others of the same kind into a larger 

 collecting duct. A number of these collecting ducts join the meso- 

 nephric duct which rims along the outer edge of the kidney. 



Fig. 123. — Photograph of a section of the bullfrog's kidney (Mesonephros), showing 

 a glomerulus surrounded by Bowman's capsule which continues into the neck of the 

 uriniferous tubule. Sections of nephridial tubules and adjoining capillaries surround 

 the renal corpuscle. 



These dift'erent portions of the tul)ules are distributed in a more 

 or less definite manner in the kidney. In the ventral region are 

 located the distal convoluted portions; in the mid-region the renal 

 corpuscles and constricted ])ortions; and in the dorsal region the 

 proximal convoluted portions and the collecting branches. The 

 adrenal gland appears as a wavy golden line located along the mid- 

 ventral siu-face. In the male, the vasa efl'erentia from the testis 

 unite with the main collecting duct along the lateral edge of the 

 kidney. The Wolffian duct, therefore, ser\-es as a sperm duct during 

 the breeding season. On the ventral surface adjacent to the renal 

 corpuscles the nephrostomes are to be found when present. 



