Adaptations of Fishes 219 



der this specialization useless or even harmful for at least a part 

 of the species possessing it. The structure then undergoes de- 

 generation, and in many cases it is brought to a lower estate than 

 before the original changes. An example of this may be taken 

 from the loricate or mailed-cheek fishes. One of the primitive 

 members of this group is the rockfish known as priestfish (Sebas- 

 todes mystinus}. In this fish the head is weakly armed, cov- 

 ered with ordinary scales. A slight suggestion of cranial ridges 

 and a slight prolongation of the third sub orbital constitute the 



FIG. 160. European Sculpin, M i/oxocephalus scorpius (Linnaeus). Cumberland 



Gulf, Arctic America 



chief suggestions of its close affinity with the mailed-cheek 

 fishes. In other rockfishes the cranial ridges grow higher and 

 sharper. The third suborbital extends itself farther and wider. 

 It becomes itself spinous in still others. Finally it covers the 

 whole cheek in a coat of mail. The head above becomes rough 

 and horny and at last the whole body also is enclosed in a bony 

 box. But while this specialization reaches an extraordinary 

 degree in forms like Agonus and Peristedion, it begins to abate 

 with Coitus, and thence through Cottunculus, Psychrolutes, Li- 

 paris, and the like, and the mailed cheek finds its final degra- 

 dation in Parliparis. In this type no spines are present any- 

 where, no hard bone, no trace of scales, of first dorsal, or of 

 ventral fins, and in the soft, limp structure covered with a 

 fragile, scarf-like skin we find little suggestion of affinity 

 with the strong rockfish or the rough-mailed Agonus. Yet 

 a study of the skeleton shows that all these loricate forms 



