of Dipnoan Fishes. 
333 
Finally, in Biscoglossus the transverse canals are reduced to 
a single one lying anteriorly and connecting testis with kidney 
duct directly. I am not aware that any morphologist would derive 
the complex testicular network so characteristic of most frogs from 
a condition such as that of Alytes : on the contrary it would be 
probably universally admitted that in Alytes we have a con- 
dition derived from that which is more usual by a reduction of 
the testicular network to a vestige at its anterior end. 
Passing then to a consideration of the conditions described in 
the two-lunged Dipnoans we find that they fall in perfectly with 
the belief that they may have come about by a similar process to 
that which has taken place amongst the Anura — that the single 
connexion between testis and kidney apparatus in Protopterus 
represents the posterior one of the metamerically repeated con- 
nexions of Lepidosiren, and that the little series of such connexions 
in Lepidosiren represents in turn the posterior members of a once 
much more extensive series, stretching through the greater part 
of the length of testis and kidney. 
I have pointed out in my paper in Proc. Zool. Soc. London, 
1901, vol. II., that it is but a step from the condition found in 
Protopterus to that found by Budgett and Jungersen in Poly- 
pterus : that the step is a very short one is indicated by what 
has taken place in the Anura. Jungersen’s work on Teleostean 
development also shows that he is justified in saying that the 
relations of testis and duct in Polypterus lead up directly to the 
relations of those structures in Teleosts. 
I believe then that the conditions shown to be present in 
Protopterus and Lepidosiren afford the strongest evidence for 
accepting in the meantime as our working hypothesis the view 
that the common ancestral forms of the various groups of gnatho- 
stomatous vertebrates possessed a well-developed testicular net- 
work, and that the cases where this is now absent have arisen 
through the enlargement of the posterior elemeut of the network 
and the atrophy of the remainder. 
