THE HEAD KIDNEYS. 



189 



diminishes in size. In 40 mm. tadpoles (Fig. So) the head kidneys 

 are less than half their former size, and the tubules are completelv 

 collapsed. By the time of the metamorphosis, the head kidnevs 



Fig. 83. — Diagrammatic figure of a 12 mm. Tadpole, dissected from the ventral 

 surface, to show the heart and branchial vessels, and the head kidneys and 

 commencing WolflSan bodies. The alimentary canal, from the oesophagus 

 to the rectum, has been removed, x 22. 



A, aorta. AF.l, AF.3, aiferent braucbial vessels of first and third brancliial 

 arches. AIi, lingual artery. CG, dilatation at the base of the lingual artery, E A, 

 communication between the afferent and efEereut vessels of the first branchial arch, by 

 further elaboration of which the carotid gl^nd win be formed. EF.l, EE.3t efferenc 

 branchial vessels of first and third branchial arches. G-M, glomerulus. KA, segmental 

 duct. KM, Wolfllan tubules. KP, head kidney. KS.l, first nephrostome. KS.3, 

 third nephrostome. LI, upper Up. L J, lower lip. LP, commencing hind limb. O A, 

 spout-like aperture of opercular cavity. OP, opercular cavity. BS, sinus venosus. 

 RT, truncus arteriosus. RV, ventricle. TC, cloaca. TO, oesophagus. TR, aperture 

 of rectal spout. 



have almost disappeared (Figs. 86 and 88), a few pigmented and 

 slightly twisted tubules alone remaining. 



All three nephrostomes disappear : the anterior one is the 

 first to close, and the middle one soon follows ; the third or most 



