490 EDWIN S. GOODRICH. 



vestigial organs of little meclianical importance, having been 

 functionally superseded by the bony rays. 



To what origin are we to trace the lepidotrichia which 

 appear in the Teleostomes ? They may be organs sui 

 generis, developed in these fish only ; or they may be derived 

 from the ceratotrichia of Elasmobranchs, as held by Ryder; 

 or, again, they may be homologous with the body-scales. The 

 evidence seems to bo strongly against the first of these views. 

 With regard to the second, it should be remembered that 

 the ceratotrichia in their development and structure exhibit 

 constant and important differences when compared with the 

 lepidotrichia; and that, as we pass from the higher to the 

 lower Teleostomes, we can trace no distinct approximation 

 in character of the Teleostome type of ray to the Elasmo- 

 b ranch type. 



The third view is the one held by Beaudelot (2)^, Gegen- 

 baur (11), Hertwig (17), and others. Strong evidence in 

 favour of this theory, that the dermal rays of the Teleostomes 

 are of the same nature as the body-scales, is afforded by 

 their histological structure and their development. This is 

 especially the case in forms which exhibit a more primitive 

 dermal skeleton ; as, for instance, in Lepidosteus, Polypterus, 

 and Hypostoma," where, as we have seen, the parallelism in 

 structure is complete, down to the possession of more or less 

 transient denticles on the outer surface. 



It is true that in the higher Teleostean fish, with thin 

 lamellatcd scales, the divergence between the two sets of 

 organs is very considerable ; but this may be traced to the 

 fact that, whilst the body-scales have become extremely 



' "Etablir ridentilc de structure des rayons natatoires et dcs ecailles, 

 c'cst ctablii- la parcnlc do ces deux ordrcs dc producticns." 



2 Hertwig writes : " Bei Ilypostoma und Calliclitliys besilzen die vers- 

 cliiedeiiei\ Tlicilc des Ilautskelets, die Tafeln und Schilder des llumpfes, die 

 Pljittclien und Slacliehi des sccundiiren Flossenskelets, die belegknoclieii des 

 primaren Scliultergiirtels und des Primordialcranium einen gemcinsamen 

 Ursprunir, indem sie pliylogenetiscli durcli Verschmelzung gleicliarligen in 

 diu oberfliicldiclicn cutislainellen diclit bei einander liegendcr kleinster 

 jvnochenplattclieii, die je ein Zahncben fragcn, enlsiaiid(n siiid" (17). 



