8 The Ganoids 
though perhaps Amia may be found to resemble the Teleostei 
in this particular. 
‘““(4) A pronephros of the Teleostean type present in the 
larva. 
‘“(s) Thalamencephalon very large and well developed. 
‘“(6) The ventricle in the posterior part of the cerebrum is 
not divided behind into lateral halves, the roof of the undivided 
part being extremely thin. 
“ (7) Abdominal pores always present. 
“The great number of characters just given are amply 
sufficient to differentiate the Ganoids as a group; but, curiously 
enough, the only characters, amongst the whole series which 
have been given, which can be regarded as peculiar to the Ganoids 
are (1) the characters of the brain, and (2) the fact of the ovi- 
ducts and kidney-ducts uniting together and opening by a 
common pore to the exterior. 
“This absence of characters peculiar to the Ganoids is an 
indication of how widely separated in organization are the 
different members of this great group. 
“At the same time, the only group with which existing 
Ganoids have close affinities is the Teleostei. The points they 
have in common with the Elasmobranchii are merely such as 
are due to the fact that both retain numerous primitive verte- 
brate characters,* and the gulf which really separates them is 
very wide. 
“There is again no indication of any close affinity between 
the Dipnoans and, at any rate, existing Ganoids. 
“Like the Ganoids, the Dipnoans are no doubt remnants of 
a very primitive stock; but in the conversion of the air-bladder 
into a true lung, the highly specialized character of their limbs,t 
their peculiar autostylic skulls, the fact of their ventral nasal 
openings leading directly into the mouth, their multisegmented 
bars (interspinous bars) directly prolonged from the neural 
and hemal and supporting the fin-rays of the unpaired dorsal 
* As instances of this we may cite (1) the spiral valve; (2) the frequent 
presence of a spiracle; (3) the frequent presence of a communication between 
the pericardium and the body-cavity; (4) the heterocercal tail. 
+ Vide F. M. Balfour, ‘‘On the Development of the Skeleton of the Paired 
Fins of Elasmobranchs,”’ Proc. Zool. Soc., 1881. 
