448 ADAM SEDGWICK, 
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 Wolffian 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 into 
the collecting part of the primary tubule and into the body 
cavity. The remaining dorsal tubules have an equally obscure 
origin. 
' « Klasmobranch Fishes,’ p. 260 e¢. seg. 
= Loe. cit. 
