434 



Comparative Morphology of Chordat* 



general, the less specialized fishes are physostomous and the highly 

 specialized forms, such as the "headfish" and sea horse (Fig. 337: 7,9), 

 are physoclistic. But there are many exceptions. It seems clear that 

 the permanence of the duct of the air-bladder is not a sufficiently 

 "conservative" characteristic to give it more than very limited or 

 "short-range" significance in classification. 



re 



Fig. 336. Weberian apparatus of the cat- 

 fish, Macrones nemerus. (A) The Weberian 

 ossicles. (B) Portion of the skull, the otic 

 labyrinth, and Weberian apparatus diagram- 

 matically represented from above, (ab) Air- 

 bladder; (av) anterior vertical canal of the 

 ear; (cl) claustrum; (eo) exoccipital; (h) hori- 

 zontal canal; (in) interclarium ; (pto) pter- 

 otic; (s) sacculus; (sa) endolymphatic sinus; 

 (sc) scaphium; (tr) tripus; (ut) utriculus; 

 (vc) vertebral column. (After Bridge and 

 Haddon. From Goodrich, "Studies on the 

 Structure and Development of Vertebrates." 

 By permission of The Macmillan Company, 

 publishers.) 



The living members of Chondrostei, Polypterini, and Holostei, 

 taken together, are usually regarded as representing eight genera. 

 These genera are all narrowly restricted in their distribution and their 

 members are not numerous anywhere. In contrast, the number of 



