370 Evolution and Distribution of Fishes 



families show striking affinities with the Ophiocephalidae, 

 and they all agree in having a superbranchial respiratory 

 or accessory gill cavity, that enables some of them to 

 breathe air directly. This is specially true of the climbing 

 perch. There seems also to be a progressive tendency to 

 the formation of an increasing number of fin-spines, from 

 the Ophiocephalidae in which they are absent, to the 

 Anabantidae in which the dorsal, ventral and anal are more 

 or less spine-rayed, then to the Osphromenidae, in which 

 the genus Betta has none, others like Osphromeniis may 

 have as few as 2 or as many as 13 spines in the dorsal fin. 



The group of three families that ichthyologists have 

 united as the Anacanthini or Gadiformes form a puzzling 

 series whose affinities and evolution seem as yet difficult 

 to trace. With the exception of the genus Lota all are 

 marine fishes. 



In proceeding from the present series of soft-finned 

 teleosts just dealt with, to those with spiny fins that are 

 treated of in the next chapter, several noteworthy and coinci- 

 dent changes gradually occur that deserve emphasis here. 

 First: attention has repeatedly been drawn in preceding 

 pages to the fact that when teleosts pass either into the 

 sea, or upward into the agitated waters of alpine streams, 

 reduction in size of the swim-bladder to the point of com- 

 plete absorption frequently takes place. Second: In pass- 

 ing from the soft-finned to the spiny-finned groups, steady 

 increase in the number and distribution of the dorsal fin- 

 spines proceeds, often also in the spines of the pelvic and 

 anal fins. So instead of only 1-3 anterior dorsal spines, as 

 in some families and genera like Percopsis and Columbia, 

 or Gastrosteus and Spinachia, most or all of the dorsal rays 

 may become so modified. Third: while, in the ganoids and 

 in nearly all of the teleosts already reviewed, the pectoral 

 and the pelvic fins are distant from each other, the former 

 occupying a thoracic and the latter an abdominal position, 

 a shifting forward of the latter takes place, till they are 

 sub-thoracic, thoracic or even jugular in position. Already 

 we have dealt with some prophetic types, like the Percopsi- 

 dae (p. 364) and Gastrosteidae (p. 366), in which such 

 transition is taking place; while those treated in next chapter 



