THE DERMAL FIN-EATS OF FISHES. 513 



branched, bony, dermal rays, developed outside the actino- 

 trichia. They bear, in primitive forms, the closest resem- 

 blance to the body-scales, and I propose to call them the 

 lepidotrichia. They have doubtless arisen through the 

 modification of scales, v^^hich must have spread over the 

 whole web of the fins. In the primitive Teleostomes the 

 lepidotrichia are very numerous, and often extended into the 

 body by means of a loug proximal unjointed piece passing 

 below the body-scales. This proximal segment is more 

 developed in the Orossopterygii than in the Actinopterygii, 

 and more developed in those Orossopterygii in which the tail 

 is scarcely heterocercal, and in which the body-scales are 

 more or less cycloid, than in the Osteolepidte. It is best 

 developed of all amongst those forms, like the Holoptychiidte, 

 with acutely lobate paired fins. 



In the Dipnoi are found jointed, branched, dermal rays, of 

 bony substance, containing bone-cells. The name campto- 

 trichia is provisionally given to these rays, which appear to 

 be in a degenerate condition in the highly modified living 

 forms Lepidosiren and Protopterus, and even to some extent 

 in Ceratodus. The camptotrichia are always provided with 

 a proximal nnsegmented region, deeply embedded in the 

 body and covered by the body-scales. Scales also extend 

 over the whole or the greater part of the fins, overlying the 

 dermal rays. 



The evidence derived from a comparison of the Dipnoi with 

 other fish appears to favour the view that the camptotrichia 

 represent the lepidotrichia of the Teleostomes. 



Assuming that the lepidotrichia have originated from 

 modified scales, it may be held that the Dipnoi with their 

 camptotrichia have been derived from ancestral forms with 

 lepidotrichia, and that the rays have become somewhat 

 degenerate, have sunk below the surface, and have become 

 covered over by a secondary extension of the body-scales on to 

 the fin, as seems to have happened quite independently in 

 some Teleosts. Such early ancestors would presumably be 

 Teleostomes with amphistylic skulls, a small hyomandibular, 



VOL. 47, PART 4. — NEW SERIES. KK 



