102 JESSE LE ROY CONEL 



tion taken at random) and average 0.0081 mm. in diameter. Be- 

 sides the giant corpuscles, there are many large nuclei in the cen- 

 tral mass which are stained about the same as the nuclei of the 

 tubules and which contain very many small granules. The giant 

 blood corpuscles resemble those in Bdellostoma, but, in the lat- 

 ter animal, they are not nearly as numerous as in Myxine. In 

 this posterior region of the pronephros of Myxine the central 

 mass resembles a lymphatic structure. 



Another striking difference between the pronephros of Myxine 

 and that of Bdellostoma is the presence of broad bands of con- 

 nective tissue which extend across the lumen of the pronephric 

 vein from side to side, and partially or completely divide the 

 lumen longitudinally in two parts (fig. 36). These bands are 

 present in all the pronephroi of Myxine, from the youngest to 

 the oldest, and are not confined to any particular region of the 

 pronephros. In one place, near the Malpighian body of the 

 pronephros, a large, isolated, thick-walled duct begins blindly in 

 such a band, continues in it for 16 sections and ends bhndly. 

 This duct has, on one side, the columnar cells characteristic of 

 the central duct, on the other the appearance of a Malpighian 

 body. From its posterior end a small tubule is given off which 

 extends alongside the duct for five sections then ends blindly. 

 The entire structure measures 0.24 mm. long by 0.195 nma. wide. 

 In another Myxine a similar duct arises in one of these bands of 

 connective tissue, extends posteriorly in it for 24 sections (0.36 

 mm.) and ends blindly at the side of a structure represented in 

 figure 38, without connecting with a tubule which extends from 

 the posterior end of the latter. These structures in the bands of 

 connective tissue are interpreted as degenerating Malpighian 

 bodies. Bowman's capsule is still present, and the tubules are 

 connected with this, but the glomerulus is almost entirely gone. 



Malpighian body of the pronephros. At least one Malpighian 

 body is always found lying beside the posterior end of the proneph- 

 ros of Bdellostoma and Myxine. Investigators of the head- 

 kidney of Myxinoids differ as to what part of the excretory sys- 

 tem this Malpighian body belongs. W. Miiller's figure 2 shows 

 two of them in the pronephros. He failed to state directly 



