THE DERMAL FIN-RAYS OF FISHES. 473 



It is to be noticed that, as a rule, iu tlie caudal fin of 

 Teleosts (the morphological ventral caudal lobe) the proximal 

 ends of the lepidotrichia are not, for the most part, attached 

 to the extremities of the endo-skeletal supports ; but have 

 pointed^ unjointed, terminal regions passing inwards on either 

 side of tlie hypural bones or hasmal spines (figs. 59 and 25). 

 The articulation of the lepidotrichia in the middle regie u of 

 the caudal lobe is often more like that of the other fins, than 

 near the edges. It will afterwards be seen that this pecu- 

 liarity of the caudal lepidotrichia probably represents a more 

 primitive condition retained and emphasised in relation to the 

 stiff, unbending character of the caudal fin, which enables the 

 Teleostean fish to swim so actively with its tail. 



But there are two entirely different kinds of dermal rays 

 in the fius of adult Teleostean fish. As was first pointed out 

 by la Valette St. George, there are in the " adipose dorsal 

 fin^' of Salmonidfe and Siluridas no lepidotrichia, but slender, 

 unjointed, horny fin-rays essentially like the ceratoLrichia of 

 Elasmobrauchs. Moreover at the distal free edge of all the 

 fins of the Teleostei similar slender horny fin-rays are to be 

 found (Lotz [24], Hertwig [17] , Harrison [13]). It was long 

 ago noticed by Agassiz (1) that the delicate median and paired 

 fius of Teleostean embryos are supported by numerous fine, 

 hair-like, dermal rays. Only at a comparatively late stage do 

 the jointed lepidotrichia develop. Vogt (40), Lotz (24), 

 Beaudelot (2), Hertwig (17), Macintosh and Prince (25), 

 Ryder (32), and Harrison (13) have since observed these rays 

 both in the embryo and in the adult. To Ryder we owe the 

 convenient name actinotrichia, which is now generally 

 applied to them. 



Lotz believes that the actinotrichia give rise to the lepido- 

 trichia by coalescence and growth. Hertwig speaks of them 

 as being involved in the formation of the adult ray, and 

 Ryder adopts the same view. Harrison, who has lately, iu 

 an admirable paper (13), given a detailed account of the 

 development of both kinds of dermal rays from their very 

 first appearance in Salmo, shows that they arc of inde- 



