185 | 
Of the Teleostei nothing need be said: everybody is agreed as 
to their derivation from, and close relations to the Ganoidei. 
The Dipnoi (and Amphibia) present greater difficulties, and 
one can see clearly but few, and mostly only negative, facts about 
their origin. We have seen reason for seriously doubting their rela- 
tionships to Ganoidei, recent or extinct. Their ancestors were either 
Selachian or, what is more probable, Proto-Selachian ancestors’ of that 
sub-class. 
They arose from fishes which possessed a better developed fore- 
brain that than of the Ganoidei, a Miillerian duct, and no swim- 
bladder. The Amphibia had the same ancestry, though when or 
where the separation took place is a moot question; either in or pre- 
vious to the carboniferous period. 
In its comparative anatomy and histology, except for the presence 
of scales and fins, and in its mode of life’), Protopterus is comple- 
tely Amphibian. Any competent observer examining in section almost 
any tissue of Protopterus under the microscope, would, if he did not 
think of the existence of a sub-class of Dipnoi, unhesitatingly pro- 
nounce it to be Amphibian ?). 
On the whole I regard the Dipnoi as now and in all past 
time perennially aquatic Amphibia, which, as they never took to the 
land, did not need to form limbs like those of other Amphibia. 
1) The cocoon-,,hibernation“ of Protopterus finds its parallel in the 
wintering in mud of ordinary Amphibia, as exemplified by Triton. The 
difference is due to the direct influence of the environment in the case 
of Protopterus, i. e. complete drying-up of the surrounding water. Last 
summer Mr. J. C. Mrrcuett, of Edinburgh, drew my attention to the 
mode in which Protopterus moves its limbs. Even in this respect the 
animal resembles an Amphibian, for it moves its fore limbs (and its hind 
limbs) one after the other forwards and then backwards, first the right 
one then the left one, just as a Proteus or Triton progresses in walking. 
2) In these pages I have not troubled to quote much of the literature 
of morphology in its bearings on the conclusions recorded here. I have 
laid great stress on the morphology of the brain as an important factor 
in determining the affinities of various groups of Vertebrates. Regarding 
the relationships of Dipnoi and Amphibia I cannot resist mentioning a 
recent statement of Prof. H. F. Oszorn’s, and cite it with the remark 
that what I have myself seen of other points in the structure of the 
brain of Protopterus is quite in agreement with this morphologist’s con- 
clusions. Ossporn, after a comparison of the Urodele and Dipnoan 
brain, concludes ,,that there is a very close similarity between the Am- 
phibian (Urodele) and Dipnoan brain, both in the external and internal 
structure“. Oszory, H. F. „Internal structure of the Amphibian brain“, 
Jour. Morph., Vol. II, 1888, p. 84. 
