464 PROF. ST. GEORGE MIVART ON THE 
Again, since in the Sharks the limbs are formed by the differentiation and predo- 
minant growth of two portions of such an, at first, continuous fold, so, as different 
species successively arose with ‘different wants and requirements, different portions of 
the fold may have been developed in different early forms’ with a resulting difference 
of innervation in such differently arising paired limbs, the resemblance between such 
diversely arising limbs being due to homoplasy. 
The results of my examinations appear to me to confirm the belief that the nature of 
azygos and paired limbs is fundamentally the same. 
I suppose no one will dispute the truth of the doctrines:—(1) that when hard sup- 
porting structures first appeared in the dorsal fin, such structures formed a longitudinal 
series of similar, separate, more or less numerous parts—a condition they still present 
in most existing fishes; (2) that more solid and complex structures in the dorsal fin 
are secondary and derivative. 
These points being concceded, have we evidence of actual coalescence in the skeleton 
of the pectoral and dorsal fins? 
Whatever view may be taken of the primitive pectoral fin (whether the archyptery- 
gium be conceived like the limb of Ceratodus, of Lepidosiren, of Raia, or as having 
arisen from diverging branchial rays), coalescence and segmentation must have taken 
place to produce the existing Elasmobranch pectoral. 
As to the dorsal fin, we have incipient coalescence between radials in Scyllium cani- 
cula (Plate LXXV. fig. 6) and Ginglymostoma cirratum (Plate LX XVI. fig. 2); and we 
have found in Notidanus cinereus (Plate LXXYV. fig. 2) a very remarkable instance of 
such coalescence, most of the radials having come to repose upon one continuous basal 
cartilage, an instance of coalescence equal to any thing found in the pectoral fin. 
Again, in Acanthias (Plate LX XVII. fig. 1), Spinax (Plate LX XVII. fig. 4), Callo- 
rhynchus (Plate LX XIX. fig. 1), Rhyncobatus (Plate LX XVIII. fig. 5), Pristis (Plate 
LXXVIIL. fig. 4), and Pristiophorus (Plate LX XVII. fig. 6), as well as in Sguatina 
(Plate LX XVII. fig. 5), we have more or less striking examples of considerable, though 
less complete or extensive, coalescence. 
But the pectoral fin has, as every one admits, the same essential nature as the ventral 
fin; and some ventral fins present a striking resemblance to dorsal fins. To see this it 
is only necessary to compare the ventral fin of Chiloscyllium (Plate LX XVI. fig. 5) 
with the dorsal fin of Raia (Plate LXXVIII. fig. 7), or the ventral of Notidanus 
(Plate LXXV. fig. 4) with its dorsal (fig. 2). 
The anal fin may also be sometimes made use of to show this community of nature 
between the azygos and paired fins. If the anal and ventral fins of Notidanus be 
compared (Plate LX XV. figs. 5 and 6), it will be difficult to believe them to be of 
radically different nature; and a comparison between the anal and ventral fins of Poly- 
! This consideration has also been brought forward by Mr. Balfour, /. c. p. 134. 
