512 EDWIN S. GOODRICH. 



We should have further to imagine, to complete our theory, 

 that the tendency amongst the Teleostomes has been for the 

 proximal embedded portion of the ray to become shorter and 

 shorter, until, in the higher Actinopterygii, it has practically 

 disappeared, except in certain regions of the caudal fin. The 

 dermal ray would then articulate, at the edge of the body, 

 with the tip of the endo-skeletal fin-support. 



The presence of actinotrichia, in addition to the lepido- 

 trichia, would not be a serious objection, since there may have 

 been several generations or layers of ceratotrichia in the 

 ancestral form. 



Conclusion. 



To conclude, we may briefly summarise some of the facts 

 dealt with above, and point out some of the difficulties which 

 remain unsolved. 



In all the fins of the true Pisces there are present dermal 

 rays of mesoblastic origin, the dermotrichia. In the Elasmo- 

 branchii and Holocephali, and probably also in the Acan- 

 tliodii and the Ichthyotomi, these rays are unjointed, occa- 

 sionally branched, and composed of a fibrous substance of 

 horny consistency without bone-cells. When denticles (placoid 

 scales) are present they are quite independent of the rays, 

 and more superficial in position. To these rays I propose to 

 give the name ceratotrichia. Their origin is unknown, 

 and for the present they must be considered as special 

 developments of the connective tissue. 



All living Teleostomes — that is to say, Polypterus (Cala- 

 moichthys ?) and the Actinopterygii (Ganoids and Teleosts) — 

 are provided with small, horny, unjointed rays at the edge of 

 their fins, to which the name actinotrichia has been given. 

 In the early stages of development these are the only dermal 

 rays supporting the fins. Actinotrichia were probably present 

 in the extinct Actinopterygii and Crossopterygii. These 

 small rays appear to be vestigial structures homologous with 

 the ceratotrichia. 



The Teleostomi are further provided with jointed, and 



