MUSEUM OF COMPARATIVE ZOOLOGY. 247 



other vein (Fig. 42, vn.jgl.) passes forward between the myotome and 

 the vagus nerve. It evidently is one of the jugular veins, but I have 

 not been able to study its distribution in later stages, and am therefore 

 unable to state more precisely which vein of the adult it represents. 



The structure of the glomus in Bufo is far more evident than in cor- 

 responding stages of Rana. In treating of the development of the glo- 

 mus in the latter, I reached the conclusion that it arises as a simple 

 fold of splanchnopleure, into which mesenchymatic cells migrate. In 

 later stages I was able to identify the original outer sheath with a 

 distinct basement membrane, and found within this membrane a large 

 number of embryonic blood corpuscles, and occasionally certain cells 

 which resembled in their histological characters those of the sheath or 

 peritoneal layer. In Bufo the vascular system is less developed than in 

 the corresponding stage of Rana ; and, owing to the small number of the 

 blood corpuscles, the remaining cellular elements come more plainly into 

 view. The usual form of the glomus is that of a hollow peritoneal sac 

 lined with endothelium (Plate VI. Figs. 47, 49, 50), and containing scat- 

 tered blood corpuscles (Fig. 46). At the entrance to the sac the endo- 

 thelium {en'th.) is continuous with the loose mesenchyme surrounding 

 the aorta, and, in certain regions, the lumen of the latter can be traced 

 into the interior of the glomus. This organ, then, exhibits markedly 

 the character of a blood sinus, the walls of which project into the body 

 cavity. Occasionally one encounters in Bufo certain minor pocketings of 

 the peritoneal layer of the glomus, — ! invaginations into the lumen of 

 the glomus at the place, e. g., occupied by the letters ccd." (Fig. 52). 

 If the cells at the apices of such invaginations were to become detached, 

 this condition woidd serve to indicate the source of the pigmented cells 

 found in the interior of the glomus in the case of Rana, although I have 

 as yet reached no final conclusion in regard to this matter. 



In this stage the body cavity exists as a distinct lumen only in the 

 region from which the nephrostomes emerge, where it constitutes a pro- 

 nephric chamber. 



My studies on the development of the excretory organs in Bufo have 

 not extended beyond the present stage. 



C. Amblystoma. 



Plate V. Fig. 44. Plate VI. Fig. 48. Plate VTI. Figs. 53-56. 

 Plate VIII. Figs. 57-65. 



Amblystoma shows in the development of its excretory system many 

 features of similarity to the Anuran forms already described. The dif- 



