134 JESSE LE ROY CONEL 



SUMMARY 



1. A central duct is present in the pronephros of both Bdello- 

 stoma and the North American Myxine, but it is in a state of 

 degeneration in both animals. This degeneration is more ad- 

 vanced in Myxine than in Bdellostoma, so that it includes the 

 inner ends of the pronephric tubules and all parts of some of the 

 largest tubules. 



2. The 'central mass,' which lies in the pronephric vein, is not 

 a series of glomeruli, but represents the disintegrated central 

 duct (including the inner ends of tubules in Myxine). 



3. The Malpighian body of the pronephros in both Bdellos- 

 toma and Myxine is located at tlie posterior end of the pro- 

 nephros, and in appearance and structure closely resembles the 

 Malpighian bodies of the mesonephros. It is formed by the 

 fusion of two or more glomeruli. 



4. The glomerulus of the pronephros in young Myxinoids is 

 exposed to the pericardial cavity through a large opening, thus 

 resembUng a glomus. This opening becomes constricted to a 

 small tubule in adult animals. 



5. The large vein which extends along the base of each pro- 

 nephros communicates with the lumen of the central duct through 

 large natural openings. The pronephric tubules connect the 

 lumen of the duct with the pericardial cavity, and the latter 

 opens into the peritoneal cavity through the large pericardo- 

 peritoneal foramen, while the body cavity opens into the cloaca 

 through the genital pore. Thus, the vascular system is in com- 

 munication with the exterior of the body. 



6. The morphology of the pronephros does not reveal any 

 positive indications as to its function. The granular coagulum 

 in the tubules and duct suggests excretion. This question can 

 probably be determined only by physiological methods. 



7. The tubules of the pronephroi of adult Bdellostoma are 

 approximately the same diameter, while those of Myxine vary 

 in size. 



8. Each tubule in the pronephros does not represent an 

 original pronephric tubule. 



