MR. A. WILLEY ON AN APODOUS AMIA CALVA. 



89 



8. An Apodous Amia calva. By Arthur Willky, F.li.S., 

 F.Z.S., McGill University, Montreal. 



[Received March 13, 1920 : Read April 13, 1920.] 



It is knoun that a goorl many interrelated genera of fishes 

 differ from each other by the presence in one and absence in the 

 other of ventral fins. Perhaps the classic and primitive example 

 of this contrasting condition is that of the Crossopterygian fishes, 

 Polypteras and C alamo ichthys, upon tiie theoretical interest of 

 which Gegenbaur (1895) laid some stress. Calamoichthys is a 

 Crossopterygian eel, the Mastacembelida) are Actinopterjgian 

 eels (Giinther), the Muraenoids are Malacopterygian eels — all 

 lacking ventral fins. A far-removed contrast of the same kind is 

 found in the Swordfishes : IJistiophorus with ventral fins, Xiphias 

 without ; and this may serve as a sample of the rest. 



Only in a few species lias the absence of ventral fins been noted 

 as a rare mutation. Brindley (1891) recorded the capture, in the 

 River Cam, of a White Bream without ventral fins. Ten years 

 later, Eigenmann and Cox (1901) described a specimen of the 

 Yellow Catfish {Amiurus natalis) from Turkey Lake, Indiana, 

 showing absence of all trace of ventral fins. Some further 

 references will be found in Gemmill (1912). 



Last November (1919) a male Amia calva, which had been 

 caught in the Richelieu River on the south side of the St. Lawrence 

 in the province of Quebec, v\as purchased from the market in 

 Montreal. Its length was twenty inches and it v\'as ni perfect 

 condition except for one strange defect, the utter absence of the 

 ventral fins. The specimen is preserved in the Peter Red[)atli 

 Museum, McGill University. The addition of Amia to the 

 meagre list of occasional apodous mutants should contribute 

 towards the ultimate evaluation of the phenomenon. Its rarity 

 and incidence show that the absence of ventral fins from fishes 

 which normally possess them is rio ordinary malformation, though 

 there is at present no means of testing its behaviour as a unit 

 character experimentally. 



Gegenbaur gave reasons pointing to the ventral fins of i-ecent 

 ganoids and teleosts having lost at least part of their original 

 function and being consequently in a state of flux and retro- 

 gression. In most teleostomes they seem to persist because they 

 have been inherited, rather than for any particular use they may 

 be to the animal. Accordingly their loss would not react in- 

 juriously upon the organism, but might be an advantage to it. 

 Bateson (1894) made no attempt to deal with this remarkable 

 variation, doubtless through lack of corroborative data. With 

 the increase of instances it seems likely that it will take its 

 place as a standard illustration of natural mutation amongst fishes, 



