4 The Ganoids 



group, while others have shown that the Ostracophori and Arthro- 

 dira should be placed far from the garpike in systematic classi- 

 fication. Cope, Woodward, Hay, and others have dropped the 

 name Ganoid altogether as productive of confusion through 

 the many meanings attached to it. Others have kept it as 

 a convenient group name for the orders of archaic Actinopteri. 

 For these varied and more or less divergent forms it seems con- 

 venient to retain it. As an adjective "ganoid" is sometimes 

 used as descriptive of bony plates or enameled scales, some- 

 in the sense of archaic, as applied to fishes. 



Are the Ganoids a Natural Group ? Several writers have 

 urged that the Ganoidei, even as thus restricted, should not be 

 considered as a natural group, whether subclass, order, or group 

 of orders. The reasons for this view in brief are the following: 



1. The group is heterogeneous. The Amiidaz differ more 

 from the other Ganoids than they do from the herring-like 

 Teleosts. The garpikes, sturgeons, paddle-fishes likewise di- 

 verge widely from each other and from the Pal&omscida and 

 the Platysomida. Each of the living families represents the 

 residue or culmination of a long series, in some cases advancing, 

 as in the case of the bowfin, sometimes perhaps degenerating, 

 as in the case of the sturgeons. 



2. Of the traits possessed in common by these forms, several 

 (the cellular air-bladder, the many valves in the heart, the 

 spiral valve in the intestine, the heterocercal tail) are all pos- 

 sessed in greater or less degree by certain Isospondyli or allies 

 of the herring. All these characters are still better developed 

 in Crossoptergyii and Dipneusti, and each one disappears by 

 degrees. Of the characters drawn from the soft parts we can 

 know nothing so far as the extinct Ganoids are concerned. 



3. The optic chiasma, thus far characteristic of Ganoids 

 as distinct from Teleosts, may have no great value. It is urged 

 that in closely related species of lizards some have the optic 

 chiasma and others do not. This, however, proves nothing 

 as to the value of the same character among fishes. 



4. The transition from Ganoids to Teleosts is of much the 

 same character as the transition from spiny-rayed to soft- 

 rayed fishes, or that from fishes with a duct to the air-bladder 

 to those without such duct. 



