468 EDWIN S. GOODRICH. 



rays belonging to the dermal skeleton. 0. Hertwig, in a 

 series of most important papers on the dermal skeleton of 

 fish (17), contributed numerous observations on the structure 

 and development of the rays, and clearly established the 

 homology of the jointed bony rays of the Actinopterygii with 

 the body-scales. Beandelot (2) had previously put forward 

 the same view, and had given a clear general account of the 

 development of the dermal rays in Teleosts, which subject 

 has again been most successfully studied in detail by 

 Harrison (13). An interesting general discussion of the 

 dermal rays has been published by Ryder (32), in which he 

 upholds the view that they are homologous throughout all 

 the groups of fish in which they occur. Pander (27 and 28), 

 Traquair (35, 36, 37), A. Smith Woodward (42), and others 

 have from time to time contributed many important observa- 

 tions on the fin-rays of extinct forms. 



Before describing the dermal fin-rays of the true Fish, it 

 may be mentioned that real dermal rays are absent in 

 Amphioxus and the Cyclostomes. The ray-like structures 

 figured and described by various authors in the larva of 

 Amphioxus (Hatschek [16], Lankester and Willey [23]) are 

 elongated epidermal cells. They have nothing to do with the 

 dermal rays of fish. In the Cyclostomes, on the other hand, 

 the fins are supported by delicate cartilaginous rays, prolonga- 

 tions of the neural and ha)mal arches of the axial cndo- 

 skeleton.^ 



Elasmobranchii. 



It is well known that the fins of the Elasmobranch fish, 

 whether paired or unpaired, are provided with so-called 

 '' horny fin-rays." These rays are slender, flexible, cylindrical 

 rods of fibrous substance, deposited in concentric layers. 

 They are pointed at the proximal end, and gradually diminish 



' Dermal rays are fii^urcd by mistake in the adult Bolellostonia by B. Dean 

 (8). It would be interesting to know whether there are any traees of such 

 rays in the youi.f,'. 



