WOLFFIAN DUCT AND BODY IN THE CHICK. 29 



cell mass which connect the muscle plate cavities with the general 

 body cavity ; and Balfour has now given his adherence to this 

 view ('Comp. Embryology/ vol. 2, p. 570). 



These canals having lost their connection with the body cavity 

 of the muscle plates acquire an opening into the segmental duct, 

 and differentiate^ into the typical WoMan tubules. The connec- 

 tion with the general body cavity may or may not be retained in the 

 adult. The secondary tubules develop as outgrowths from that 

 part of the primary tubules, which will give rise to a Mal- 

 pighian capsule. These outgrowths grow forward and even- 

 tually acquire an opening into the terminal portion of the 

 tubule of the segment in front. Later they loose their connec- 

 tion with the Malpighian capsules, though a rudiment of this is 

 sometimes retained as a solid cord of cells. 



The method of development of the secondary, tertiary, &c., 

 tubules has not been followed. 



The primary tubules open into the segmental duct very shortly 

 after the latter has acquired an opening into the cloaca. 



The formation of the Malpighian bodies and the outgrowths 

 from them to form secondary tubules occur later. 



For a full account of the development of the mesonephros 

 in Elasmobranchs I must refer to the works of Balfour and 

 Semper, to whom we owe the whole of our knowledge. 



Development of the Mesonephros in the remainder of the 

 Ichthyopsida, 



As a type of this development I will take an Amphibian, 

 Salamandra, in which animal it has been more completely 

 elucidated by Fiirbringer than in any other.'^ 



Fiirbringer describes the formation of the mesonephros as 

 taking place entirely during larval life; no trace of the gland 

 being seen in the newly hatched larva. It arises as a series of 

 ingrowths of the peritoneal epithelium, which soon become 

 separate from the latter. The primary tubules are hollowed out 

 in the cell masses so formed independently both of the body 

 cavity and segmental duct (Wolffian duct), but subsequently 

 they acquire an opening into both. 



The secondary tubules arise in a blastema, the origin of 

 which is not clear, but is apparently derived from the just 

 mentioned serial ingrowths. They acquire an opening mto 

 the collecting part of the primary tubule and into the body 

 cavity. The remaining dorsal tubules have an equally obscure 

 origin. 



' ' Elasmobranch Fishes,' p. 260 et. seq. 

 ' Loc. cit. 



