46 



ADAM SEDGWICK. 



step between them is not great.* It is merely necessary to 

 suppose the division of the glomerulus (in fig. 24) into two 

 parts, and a simultaneous development of certain folds from the 



ti'.of — a 



Wolffian duct to form the tubules, and the original single 

 tubule would have been transformed into a ventral primary 

 and a dorsal secondary tubule. 



Further, as I have pointed out in another paper,^ the secon- 

 dary tubule always arises in close proximity, apparently from 

 a blastema continuous with a part of that from which the 

 primary tubule arose. 



A modification of development is to be expected, because in 

 those animals in which the mesonephros develops after hatching, 

 it clearly comes gradually into use. The whole is not wanted 

 at once, but with the increasing size of the larva, more tubules 

 are wanted. The first developed (primary) in Salamandra 

 acquire a structure with which they can apparently perform 

 their function when there is hardly a trace of the secondary 

 tubules (Fiirbringer, loc. cit., fig. 26). 



' It will be observed that in this figure the tubule connecting the 

 WolflBan duct, and capsule is hardly developed. In all probability, this was 

 on tlie analogy of the pronephros, the primitive state of things, the tubule, 

 being a secondary differention of the duct near each glomerulus. 



' ' Quart. Jouru. Micr. Sci./ April, 1880. 



