SCALE OBSERVATION'S OF THE SOUETEAGUE AND PIGFISH. 3 13 



(5) Apparentl_\- the scales of some fish do not calcify so rapidh- as those of others. 

 Synodus faetens has very thick and broad scales; nevertheless they are not marked with 

 so many radii as might be expected. They are calcified very little in comparison with 

 those of Archosargus probatoccphalits. In fact, judging from the flexibility of these 

 scales, one would expect still fewer radii were it not for convexity. 



(6) Most scales are more or less meniscus in shape, the convex side being exterior. 

 This is believed to be responsible for the radiate rather than a transverse direction of 

 the radii. If a scale were perfectly flat, fewer radii would appear, and they would run 

 perpendicular to the long axis of the body of the fish. The more depressed the body of 

 the fish, the more convex the scale, and consequently the more sculptured with radii. 



Brevoortia tymnnus furnishes an example of a scale that is nearly flat. On this 

 scale the radii are irregular in direction and are generally perpendicular to the long axis 

 of the scale. 



(7) The scale acts as a lever. When the posterior side is raised, the center rests 

 against the upper edge of the scale pocket as a fulcrum, and the anterior edge is pressed 

 inwardly. It is easily seen, then, that the more posterior the fulcrum — i. e., the more 

 deeply inserted the scale — the more numerous the radii. As a further substantiation 

 of this theory, it has been possible to tear the several laminae apart. The segments 

 between two radii of the upper laminae were completely separable from the surrounding 

 tissue, indicating that they were not held in place by the tissue of the laminae from 

 which they were taken, but by the stratum below. In the upper laminae the scale 

 being stiffened by calcification, broke into separable segments, while the uncalcified 

 stratum below yielded when the scale was bent. 



There are probably numerous other factors influencing the presence, number, and 

 character of the radii. Among these might be mentioned the elasticity of the scale 

 pocket. This is probably less in older fish than in young, with a concomitant increase 

 in the number of radii. The shape of the body of the fish, its length, comparative 

 activity, and habits may be more or less important influences. 



With this large number of variants contributing to the production or nonproduction 

 of radii, their value as taxonomic characters appears very doubtful. For instance, it 

 is certain that the scale grows more anteriorly than posteriorly, being forced deeper and 

 deeper into tfie pocket, throwing the fulcrum posteriorly, tending to produce more radii. 

 It also increases in size, again necessitating more radii. At the same time, calcification 

 is going on, making the scale less flexible, and its thickness is increasing by the constant 

 addition of secretions from below, the shape remaining practically constant throughout 

 life. All these conditions tend to a geometrical increase in the number of radii. But 

 while the fish is growing older, its activity is possibly declining, tending to reduce the 

 number of radii. Distention consequent upon spawning may be another factor, increas- 

 ing or diminishing the number of radii. These variants may conflict and neutralize, 

 or may work together to increase the number of radii. From all this we may conclude 

 that bj' simply counting the radii without taking the contributing factors into considera- 

 tion, fallacious conclusions may be reached. 



Some of these factors are, however, taken into consideration in taxonomy. The 

 shape of the fish is always noted. The size (number of scales in a line) and shape of 

 scales are also noted. If now, instead of counting the radii, the other factors of elasticity 

 and thickness were considered, we would have much more reliable additions to ordinary 

 characters in classification. 



