1890.] The Homologies of the Fins of Fishes. 413 
the view of Huxley that the fins of Ceratodus represent the archi- 
pterygium or primitive paired fin, as distinguished from a primi- 
tive lateral continuous fin, which the theory of Balfour leads us 
to anticipate may be yet discovered, and which is partly realized 
in the extinct genus Climatius. And whatever homology may be 
traced between the paired and median fins, it is evident that the 
axis of the former has undergone changes which the latter have 
not experienced. This consists in the sliding proximad of some 
of the lateral branches of the axis, so that there came to be two, 
three, or more axial pieces attached to the point of support or 
scapula. The primitive type is termed by Huxley unibasal, and the 
later type pluribasal. In the Elasmobranchii the paired fins are 
unibasal in the Ichthyotomi, and pluribasal in the Selachii. In 
the Holocephali all are pluribasal. In the Dipnoi the known 
forms are univasal. In the Crossopterygia the majority are uni- 
basal, but the order of Cladistia (Polypteride) are pluribasal, 
having two or three (as they are counted) axial bones articulating 
with the scapula. In other Teleostomata the paired fins are 
pluribasal, and have mostly lost the axial elements, the basilars 
only remaining (Fig. 4). 
In any case the connection of the paired fins has not been 
traced to the vertebral axis, as is the case with the median fins, 
the scapular and pelvic arches being their support in the earliest 
stages and oldest types known. This has been completely estab- 
lished by the recent researches of Wiedersheim,” as far as em- 
bryology alone can do it. 
As the case at present stands, whatever of proof morphology 
or embryology furnishes, is in favor of the similar origin and 
homology of the vertical and paired appendages, but that their 
relations with the skeletal axis are not identical. 
3. ON THE NATURE OF THE SUPPORTS OF THE MEDIAN FINS. 
In my memoir on the Fishes of the Lesser Antilles of 1870,” 
as already remarked, I have called attention to the systematic 
significance of the connection of the fin radii with the vertebral 
= BA scr tesa Anzeiger, 1889, No. 
Transactions of the American Philosophical Society, p. 450. 
