36 bulletin: museum of comparative ZOiJLOGY. 



origin of the mesonephric elements, but is inclined to think that they are 

 derived from the peritoneum. 



As was pointed out above, such an origin of the mesonephric units 

 would not be incompatible with the existence of a mesonephric funda- 

 ment (the mesomer) homologous throughout the vertebrate series, and 

 would even seem to be fairly well established for Petromyzon (Wheeler, 

 '99). The fact of such an origin in Amphibia has, however, been dis- 

 puted by Marshall and Bles ('90). Although they were unable to 

 decide as to the true origin of the mesonephric fundaments, they were 

 certain that these do not arise from the peritoneum and that the nephro- 

 stomes join them secondarily. 



The first problem, then, is that of the origin of the mesonephric funda- 

 ments and the question as to whether or not both layers of the mesoderm 

 enter into it. 



The origin of the dorsal sets of units seems never to have been care- 

 fully investigated. Spengel ('76) thought they arose by a splitting of 

 the Malpighian body of the primary units. Fiirbringer ('78) states that 

 their origin is similar to that of the primary, which he describes as 

 developing (at least in the case of the more anterior units) from solid 

 peritoneal outgrowths, Hoffmann ('86) came to the conclusion that they 

 are derived from the primary units because they equal them in number. 



Material and Methods. 



I have no reason to doubt that all of the urodele material on which 

 the investigation of the mesonephros is based consists of Amblystoma 

 punctatum Linn., as that is the only species of Amblystoma at all common 

 about Cambridge, Massachusetts, where the eggs were collected. The 

 male and female animals of this species were often found in the ponds 

 where the eggs were collected. Two females of the species named, when 

 brought home, laid freely in captivity ; and the developing embryos and 

 larvae differed in no respect from any of those collected from the ponds. 

 The large translucent masses of jelly containing the eggs are attached to 

 twigs and rushes about a foot beneath the surface of the water. In the 

 near neighborhood, the white, fungus-like spermatophores can generally 

 be seen dotting the twigs and leaves of the bottom. The eggs are laid 

 as soon as the ice is well out of the ponds. 



The Amblystoma material which was used in the study of the Miiller- 

 ian duct was mostly collected at New Haven, Connecticut. It consists 

 of larvae in their second year. The majority were caught early in May 



