106 JESSE LE ROY CONEL 



true glomus. In each of his youngest Myxine he found a very 

 large opening connecting the capsule with the pericardial cavity; 

 it extended through almost as many sections as the glomus it- 

 self. But in advanced stages, by a folding of the epithehal wall, 

 a capsule is formed around the glomus, and only a slit-like com- 

 munication with the pericardial cavity is left, and even this may 

 be completely closed. The glomerulus of the youngest Mjocine 

 examined by the writer (no. 18) lies directly exposed to the peri- 

 cardial cavity through an opening 0.156 by 0.192 mm. and re- 

 sembles a glomus (fig. 43). The opening in Myxine no. 15, an 

 adult, measures 0.0195 by 0.105 mm., and that of Myxine no. 

 10, the oldest specimen, is 0.195 by 0.120 mm. 



The glomerulus of the head-kidney is not always as large in 

 comparison with the glomeruli of the mesonephros as would be 

 expected if it were formed by the fusion of two or three glomeruli, 

 as the following measurements will indicate; see opposite page. 



The figures 1, 2, 3, 4 in the column under 'Glomerulus' repre- 

 sent the number of the glomerulus, counting that of the head- 

 kidney as 1 ; glomeruh 2, 3, and 4 are the first, second and third 

 glomeruli, respectively, of the mesonephros immediately follow- 

 ing the glomerulus of the pronephros. All the glomeruli which 

 lie posterior to the glomerulus of the pronephros are considered 

 as belonging to the mesonephros. The glomeruli of the latter, 

 posterior to the most anterior three or four gradually diminish 

 in size. None of the anterior glomeruli of the mesonephros of 

 Myxine were sectioned, therefore no measm'ements of these are 

 given in the above table. As the table shows, the glomerulus of 

 the pronephros does not always exceed or even equal in size some 

 of the most anterior glomeruU of the mesonephros. 



As has already been noted, the Malpighian body of the pro- 

 nephros of one Bdellostoma (fig. 12) is connected by tubules to a 

 fragment of the segmental duct of the mesonephros, which is en- 

 tirely disconnected from the continuous part of the duct. No 

 other case of a communication between the Malpighian body of 

 the pronephros and the duct of the mesonephros was found in 

 either Bdellostoma or Myxine. In a young male Bdellostoma 

 (no. 22), however, the mesonephric duct on each side continues 



