190 



THE FROG. 



posterior one persists for a short time longer, and then in its 

 turn closes, loses its connection with the peritoneum, and 

 disappears. Shortly before the closure of the third nephrostome, 

 the head kidney separates completely from the segmental duct, 

 which then ends blindly in front. 



The glomerulus of the head kidney (Figs. 83, 84, gm) arises, as 



V.4 X 



Fig. 84. — Transverse section across a 12 mm. Tadpole ; the section passing- 

 through the middle of the length of the head kidney, x 44. 



A, aorta. AP, pulmonary artery. BH, medulla oblongata. CH, notochoril. 

 GI, portion of a gill. GM, glomerulus. KP, tubule of head kidney. KS, second 

 neplirostome. LA, commencing fore limb. LG, root of lungs. NY, sympathetic 

 ganglion. OP, opercular cavity. TI, intestine. TO, oesophagus. V.4, fourth 

 ventricle. VC, posterior cardinal vein. VH, posterior vena cava. VP, pulmonary 

 vein. "W", liver. X, ganglion of spinal nerve. X', thin roof of fourth ventricle. 



described above (p. 182), as a sacculated outgrowth from the 

 ventral and outer wall of the aorta, bulging outwards into 

 the body cavity opposite the nephrostomes. At the time of 

 hatching of the tadpole (Fig. 82) the dorsal portion of the body 

 cavity is practically the only part present : for although the 

 splitting of the mesoblast extends down the sides of the body to 

 the ventral surface, yet the two layers, somatic and splanchnic, 



