204 American Fisheries Society 



in the spines of catfishes. While still covered by skin 

 they may appear smooth enough, but after the soft tis- 

 sues are removed the surface is found broken by deep 

 and more or less longitudinal furrows with correspond- 

 ing intermediate ridges, Fig. 4. These ridges are 

 reminiscent of the ankylosis of dichotomous divisions of 

 soft rays. The spine as a whole represents a single soft 

 ray. Instead of a derivation through the suppression of 

 branches and the early co-ossification of segments, the 

 spines of catfishes ossify and become rigid after the for- 

 mation of the dichotomous branches has taken place. 

 This is clearly shown by a study of both the surface of 

 the spine and microscopical preparations. 



As a rule the anterior branch of the first soft ray in 

 a fin is the shortest one, the succeding divisions becom- 

 ing progressively longer according to the curvature of 

 the edge of the fin-web. These relations are obvious in 

 the elements of the spines of catfishes as shown in Fig. 

 4. The first ridge (fd.) on the anterior side of the spine 

 represents the first division of the ray. It extends 

 diagonally towards the anterior margin and comes to an 

 end somewhat before the middle of the spine is reached. 

 The second (sd.) division is similar in appearance and 

 course, but does not end until the distal half of the spine 

 is reached. The third (td.) is the longest of the spine 

 elements and forms the point. The fourth (fd.) 

 although not so pronounced as the other divisions is in- 

 corporated with the spine to about the middle of its ex- 

 tent at which level it fails to co-ossify with others and 

 becomes an independent division in the fin-web near the 

 margin of which it divides. The free portion of this 

 division is in every respect like that of soft rays. In 

 the proximal portion of the spine, particularly of very 

 young specimens there are numerous openings extend- 

 ing into the cavity. These represent the last vestiges of 

 the spaces between segments. As the fish matures new 

 bony tissue is deposited in the longitudinal grooves which 

 become less and less conspicuous with age. 



