STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 
409 
normal form of tail characteristic of the Teleostei, in which, however, the caudal fin 
has become very much reduced and merged into the prolongations of the anal and 
dorsal fins. 
This can be very clearly seen in Siluroid forms with an Eel-like tail, such as 
Cnidoglanis. Although the dorsal and ventral fins appear to be continuous round the 
end of the tail, and there is superficially no distinct caudal fin, yet an examination of 
the skeleton of Cnidoglanis shows that the end of the vertebral column is modified in 
the usual Teleostean fashion, and that the haemal arches of the modified portion of the 
vertebral column support a small number of fin-rays; the adjoining ventral fin-rays 
being supported by independent osseous fin-supports (interspinous bones). 
In the case of the Eel ( Anguilla anguilla) Huxley ( loc. cit.) long ago pointed out 
that the terminal portion of the vertebral column was modified in an analogous 
O 
fashion to that of other Teleostei, and we have found that the modified haemal arches 
of this part support a few fin-rays, through a still smaller number than in Cnidoglanis. 
The fin-rays so supported clearly constitute an aborted ventral lobe of the caudal fin. 
Under these circumstances we think that the following statement by Mjvart 
(Zool. Trans, vol. x., p. 471) is somewhat misleading :— 
“ As to the condition of this part ( i.e ., the ventral lobe of the tail fin) in Teleosteans 
generally, I will not venture as yet to say anything generally, except that it is plain 
that in such forms as Murcena, the dorsal and ventral parts of the caudal fin are 
similar in nature and homotypal with ordinary dorsal and anal fins.”* 
The italicized portion of this sentence is only true in respect to that part of the fringe 
of fin surrounding the end of the body, which is not only homotypal with, but actuallv 
part of, the dorsal and anal fins. 
Having settled, then, that the tails of Chimaera and of Eel-like Teleostei are simply 
special modifications of the typical form of tail of the group of Fishes to which they 
respectively belong, we come to the consideration of the Dipnoi, in which the tail fin 
presents problems of more interest and greater difficulty than those we have so far had 
to deal with. 
The undoubtedly very ancient and primitive character of the Dipnoi has led to the 
view, implicitly if not definitely stated in most text-books, that their tail-fin retains 
the character of the piscine tail prior to the formation of the ventral caudal lobe, 
a stage which is repeated embryologically in the pre-heterocercal condition of the tail 
in ordinary Fishes. 
Thiough the want of embryological data, and m the absence of really careful histo¬ 
logical examination of the tail of any of the Dipnoi, we are not willing to speak with 
very great confidence as to its nature ; we are nevertheless of the 0 | 3 inion that the 
facts we can bring forward on this head are sufficient to show that the tail of the 
existing Dipnoi is largely aborted, so that it is more or less comparable with that of 
the Eel. 
* The italics are ours. 
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