STAGE m Hi, 



SHORTLY BEFORE 

 HATCHING 



ELENCEPHALON 

 ROOT OF VAGUS NERVE 

 SOMITE n 



GANGLION NODOSUM 

 OF THE VAGUS 

 NERVE 



PRONEPHRIC TUBULE 



Fig. 346. The developing pronephric kidney in the frog, Rana sylvatica (A-C and E, 

 redrawn from Field, 1891, Bull. Mus. Comp. Zool. at Harvard College, vol. 21. E con- 

 siderably modified). (A) Transverse section through developing second pronephric 

 tubule of frog embryo at a time when the neural tube is completely closed, two gill 

 fundaments are present and the otic vesicle is a shallow depression. (B) Same tubule 

 at about the time of hatching. (C) Section through first pronephric tubule at 8 mm. 

 stage. (D) Transverse section through second pronephric tubule, see line d, fig. 346F, 

 of 18 mm. Rana pipiens tadpole. (E) Entire pronephric kidney of one side of 8 mm. 

 R. sylvatica embryo. (F) Schematic reconstruction of 18 mm. R. pipiens tadpole look- 

 ing down from dorsal area upon the pronephric kidneys and the developing mesonephric 

 kidneys, 



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