REPORT OF COMMISSIOXERS OF INLAND FISHERIES. 37 



family. The perfection of this adaptation is perhaps best seen in 

 the case of the Spanish Mackerel. Its body is spindle shaped and 

 so smoothly rounded in every part of its surface that it affords the 

 least possible resistance to the motion of the fish through the water. 

 The forward half of the fish is perfectly smooth, symmetrical, and 

 somewhat cone shaped; it serA^es admirably as a cut-water for the 

 rest of the body. It is made more perfect for this purpose by the 

 wedge-like shape of the head, all the surfaces of which are perfectly 

 rounded, and its external structures fitted together in such a way 

 that there are no irregularities or projections to break the 

 smoothness of its curves and furnish resistance to rapid progress 

 through the water. The margins of the jaws fit tightly to each 

 other, the surfaces of the eyes conform perfectly to the curvature of 

 the surfaces of the head, and the gill covers close smoothly to its sides. 

 All these parts fit together with such accurac}' that, from the apex 

 of the jaws, the surfaces bounding the head diverge gradually in 

 long, slightly convex curves and without a break pass over to the 

 body region of the fish; then, near its middle, they gradually become 

 merged into the slightly concave surfaces of the posterior region. 

 This portion of the body tapers gradually backward and ends in the 

 strong, broadly-forked tail fin; its surfaces run in 

 smooth, slightly hollow curves, which allow the water 

 displaced by the forward movement of the fish to 

 pass backward with the least resistance. A strong 

 median longitudinal ridge is developed on each side 

 of the caudal region of the trunk. This serves as a 

 horizontal keel and is supposed to prevent the stroke 

 of the tail from varying from the vertical plane. 

 When viewed from in front, the outline of the body 

 " appears as a perfect ellipse and surprisingly small 

 in size; " the margins of the fins now appear scarcely 

 the Spanish I^ck- clistiuguishable and are so sharp and thin as to offer 

 erei. (After Dean). ^.gj.y ^^^jg rgsistauce to the Water. The skin of the 

 body is perfectly smooth, since the scales are very small and with- 



