486 EDWIN S. GOODRICH. 



their surface. Hertwig long ago showed that this is also the 

 case in Siluroids and Acipeuseroids^ where the segments of the 

 lepidotinchia resemble in every detail the spiny plates and 

 scales on the body. As we pass to the more highly specialised 

 Teleosts^ with cycloid and ctenoid scales, the resemblance 

 between the segments of the rays and the body-scales becomes 

 less obvious, the lepidotrichia preserving, as a rule, a more 

 primitive and truly bony structure. But in the highest 

 Teleosts both the endoskeleton and the lepidotrichia may 

 lose the bone- cells. 



Whilst in the lowest Teleostomes, like Acipenser, the lepi- 

 dotrichia are much more numerous than the endo-skeletal rays, 

 overlap the latter to a considerable extent, and are not 

 specially differentiated at their proximal ends ; in the " bony 

 Ganoids " and the " Teleostei " they come to correspond 

 strictly in number with the endo-skeletal supports, to the small 

 distal element of which (the " baseost ") they become closely 

 connected. The proximal segment of the lepidotrichia in 

 these fish becomes enlarged and differentiated for clasping 

 the baseost and for the attachment of muscles. This modifi- 

 cation is carried out more completely in the higher than in the 

 lower forms (Polypterus), and more completely also in some 

 fins than in others (Text-fig. 4). 



4. The dermal rays of the living Dipnoi, or campto- 

 trichia, may be considered, for present purposes, as a fourth 

 and distinct variety of ray, somewhat intermediate in charac- 

 ter between the ceratotrichia and the lepidotrichia. Like the 

 former, they are much more numerous than the endo-skeletal 

 fi.n-supports, and overlap them on either side. In Ceratodns, 

 where the dermal rays are best developed, they are seen to 

 consist of a slender rod of fibrous, flexible material, which 

 acquires the appearance and consistency of fibrous bone in its 

 older and thicker parts. A large number of branching cells 

 are distributed throughout the substance of the ray, which 

 may be distinguished into an inner and an outer more 

 calcified region. The camptotrichia may branch, and nro 

 generally jointed. As a rule they arc subdivided into a tuore 



