THK DERMAL FIN-RAYS OF FISHES. 489 



With regard to the actinotrichia, their universal presence 

 ill all the widely diverging groups of Teleostomes suggests 

 tliat they are of very ancient orign. Most writers, like 

 Beaudelot (2), Ryder (32), Harrison (13), compare them to 

 the ceratotrichia. As Beaudelot says, '' Les nageoires des 



,. O.sc 



eft 



Fio. 5. — Diagrammatic section tlirou<i;Ii flie dorsal fin of Ceratodus. 

 For IcMerinp; see p. 517. 



premiers [Selachians] avec leur filaments comes pour 

 squelette, correspondant evidemment a la nagcoire embryon- 

 naire des seconds [Teleosteans]," with its "filaments cornes." 

 There can be little doubt that these two kinds of rnys are 

 homologous. Of similar shape, structure, and developinental 

 history, thoy must surely be of common oi'igiu. In adult 

 living Teleostomes, however, they would appear to be only 



