THE LATER DEVELOPMENT OF THE FROG 199 



connections of the inner tubules with the pronephric duct 

 convert this into the mesonephric or Wolffian duct, which 

 remains as the ureter of the mesonephros or definitive kidney. 

 The inner tubules elongate and become coiled, forming the 

 tubular portion of the later kidney. 



m 



B 



FIG. 73. Sections through the developing mesonephros and the common 

 nephrostome of R. sylvatica. After Hall. A. Section through the eighth somite 

 of an 8.5 mm. larva. B. Section through the mesonephric rudiment of a 25 mm. 

 larva. C. Section through the common nephrostome of a 25 mm. larva, o, 

 Dorsal aorta; c, coelom; en, common nephrostome; g, germ cell; i, inner tubule; 

 m, mesonephric rudiment; my, myotome; o, outer tubule; p, remains of prone- 

 phros; pc, posterior cardinal vein; s, shelf cutting off the common nephrostome 

 from the remainder of the ccelom; so, somatic mesoderm; sp, splanchnic meso- 

 derm; W. Wolffian duct; /, primary mesonephric tubule; //, secondary meso- 

 nephric tubule. 



Subsequently the outer tubules have a rather unusual history 

 in the frog. From the proximal portion an outgrowth appears, 

 which forms the capsule (Bowman's capsule) around the glo* 



