8 WILLIAM MORTON WHEELER, 



openings, the anterior of which is smaller than the posterior. The 

 larger opening is then converted into two short openings by a fusion 

 of its lips near the middle of its length, so that the pronephric 

 pocket now has three openings into the coelora. The portions of the 

 pocket around the lips of the openings elongate and become the 

 tubules of the pronephros. Goette could not make out how the 

 number of tubules is increased to five ("selten 4 oder 6"), but as he 

 finds the groove-like evagination of the somatic mesoderm still open 

 behind the three tubules, he believes that the fourth to fifth funnels 

 are formed in the same manner as the anterior ones. He denies that 

 there is any correspondence between the metamerism of the body and 

 that of the tubules, since he finds : "sowohl 3 als 6 Canäle im Be- 

 reich zweier oder dreier Metameren." The collecting duct later be- 

 comes coiled and finally forms a convolute with the proximal ends of 

 the tubules. During the formation of the funnels the peritoneal epi- 

 thelium on the mesial side of the pronephros bulges cut like a sac, 

 certain mesoderm cells and a twig from the aorta push their way 

 into it and thus form a more or less racemose glomerulus. The 

 tubules of the pronephros ultimately become embedded in the anterior 

 cardinal vein. The pronephric duct is completely cut ofi' from the 

 somatopleure. Goette observed considerable diftereuces in the ap- 

 pearance of the duct at difierent points during its formation. In 

 some places it appeared as a hollow diverticulum of the underlying 

 somatopleure, at other points as a solid or nearly solid cord. These 

 appearances, however, he deems of little morphological importance. 

 The extreme posterior end of the duct is said to arise from the 

 mesenteric fold of the mesoderm, and thus the way in which the 

 duct reaches the gut is explained. It should be added that Goette 

 also describes a fusion of the splanchnopleure and somatopleure just 

 below the anterior and posterior ends of the pronephros. These con- 

 strictions, which are of a transitory nature, are to Goette "un- 

 zweifelhaft" an imperfect closing off of a pronephric chamber like that 

 of the Amphibia. 



BujOR (1891) studied the pronephros of the Ammocœtes during 

 its transformation into the Fetromyson and found it to consist of three 

 or four ciliated funnels and a glomus, the tubules having disappeared. 

 In the adult Fetromyzon the pronephros "s'atrophie davantage, mais 

 toujours on en rencontre des traces". 



