48 



FISHES. 



rinally, in Sharks, the Balistidae, and others, true scales 

 are absent and replaced by the ossified papillse of the cutis, 

 which give the surface the appearance of fine-grained chagreen. 



Fig. 17. — Dermal papilla of Monacanthus trossulus. 



Fig. 18. — Dermal iJapillse of Monacanthus hippocrepis (magn.) 



These generally small bodies, as well as the large osseous 

 scutes of the Eays, Sturgeons, etc., have been comprised 

 under the common name Placoid scales ; a term which 

 deservedly is being abandoned. 



Along the side of the body of osseous fishes runs a series 

 of perforated scales, which is called the lateral line (Fig. 

 21). The perforating duct is simple at its base, and may 



be also simple at its outer 

 opening (Fig. 19), or (and this 

 is frequently the case) the 

 portion on the free surface of 

 the scale is ramified (Fig. 20). 

 Tlie lateral line runs from 

 the head to the tail, some- 

 times reaching the caudal 

 fin, sometimes stopping in front of it, sometimes advanc- 

 ing over its rays. It is nearer to the dorsal profile in some 

 fishes than in others. Some species have several lateral 

 lines, the upper one coasting the dorsal, the lower the 

 abdominal outline, one running along the middle as usual. 



Fig. 19. — Cycloid scale from the lateral 

 line of Odax lineatus (magn.) 



