332 
Mr Kerr, The Genito-ur inary Organs 
fused posteriorly across the middle line. In Protopterus, however, 
there passes off to each side only a single vas efferens which 
arises from the extreme posterior end of the fused testes. 
The presence of a testicular network in Dipnoi is of great 
morphological interest, adding as it does another to the great 
groups of gnathostomatous vertebrates in which such an arrange- 
ment occurs. These groups are the Selachians, the Dipnoans, the 
Amphibians, the Reptiles, the Birds, and the Mammals. In fact, 
the only groups in which it does not characteristically occur are 
those of the Crossopterygii, and the Teleostomi. But in the 
latter group we have only to look at those forms which the 
common consensus of Zoologists regards as most primitive — the 
Ganoids — and we here find a testicular network of the most 
typical kind ( Acipenser , Lepidosteus, Amia). There only remain 
then the higher Teleostomes, viz. the Teleostean fishes, and the 
Crossopterygians, in which the network is absent. We should, 
I think, require very strong evidence before we could believe 
that an arrangement characteristic of a single one of the groups 
of Gnathostomata, and of the admittedly more highly specialized 
members of a second group, was the primitive one amongst 
gnathostomatous vertebrates, rather than another arrangement 
which is characteristic of all the remaining groups. Evidence of 
the required weight is, I believe, completely wanting. Against 
such a view we have, in the first place, the balance of morpho- 
logical probability. We know that it is one of the most fundamental 
characteristics of the coelomata that two main functions — that 
of nitrogenous excretion and that of reproduction — are carried 
on by the cells lining the coelom, their products passing into that 
cavity. Surely it is probable that these two products should 
primitively find their way to the exterior, by the same ancient 
channels of communication of that cavity with the exterior, — the 
nephridial tubes. 
Secondly, we have the fact that the conditions in Lepidosiren 
and Protopterus when taken with certain facts in regard to other 
groups, furnish a very simple explanation of how the arrangements 
in Crossopterygians and Teleosts may have been derived from 
those common to the other groups of Gnathostomes. 
If we regard the different forms of anurous Amphibians 1 we 
find that typically there is an extensive testicular network, con- 
necting testis and kidney over a considerable part of their total 
length. In the male Bombinator the anterior transverse canals of 
the network have become enlarged, and their course to the kidney 
duct has become direct. In the male Alytes the same happens, 
but here the (usually two) enlarged canals are the sole represent- 
atives of the network. 
1 v. Gadow, Cambridge Natural History , vol. vm. p. 51. 
