50 FISHES. 



the transverse series, generally in that running from the com- 

 mencement of the dorsal fin, or the middle of the back to the 



Fig, 21. — ArrangeTnent of scales in tlie Eoach (Leuciscus ratilus) : i ? — Lateral 

 line ; t T = Transverse line, a, Transverse line from lateral line to ventral fin. 



lateral line, and from the lateral line down to the vent or 

 ventral fin, or middle of the abdomen.^ 



The scales of many fishes are modified for special pur- 

 poses, especially to form weapons of defence or a protective 

 armour, but the details of such modifications are better men- 

 tioned under the several families in which they occur. AH 

 scales are contiaually growing and wasting away on the 

 surface, and it seems that some fish, at least, — for instance, 

 Salmonoids — -"shed" them periodically; during the progress 

 of this shedding the outlines of the scales are singularly 

 irregular. 



' In the formula generally preceding the description of a fish, "L. lat. 

 40," would express that the scales between the head and caudal fin are 

 arranged in 40 transverse series ; and prohably, that the lateral line is com- 

 posed of the same number of scales. " L. transv. f " would express that there 

 are eight longitudinal series of scales between the median line of the back and 

 the lateral line, and five between the lateral line and the middle of the 

 abdomen. 



