. Entomology : with special reference to its biological and economic aspects. HydrophUus triangularis,natural size. 186 ENTOMOLOGY Locomotion.—Excellent adaptations for aquatic locomo-tion are found in the common Hydrophiliis friaiignluris (). Its general form reminds one of a boat, and its longlegs resemble oars. The smoothly elliptical contour and thepolished surface serve to lessen friction. Owing to the formof the body (Fig. 22/. A) and the presence of a dorsal air-. ^ B Transverse sections of (.-J) Hydrophilus and (S) ; /, metathoracic leg. c. eh-tron; li, hemely- cha
. Entomology : with special reference to its biological and economic aspects. HydrophUus triangularis,natural size. 186 ENTOMOLOGY Locomotion.—Excellent adaptations for aquatic locomo-tion are found in the common Hydrophiliis friaiignluris (). Its general form reminds one of a boat, and its longlegs resemble oars. The smoothly elliptical contour and thepolished surface serve to lessen friction. Owing to the formof the body (Fig. 22/. A) and the presence of a dorsal air-. ^ B Transverse sections of (.-J) Hydrophilus and (S) ; /, metathoracic leg. c. eh-tron; li, hemely- chaml)er under the elvtra. the back of the insect tends to re-main uppermost, while in Notonecta (Fig. 227, i?), on the otherhand, the conditions are reversed, and the insect swims withits back downward. The legs of Hydrophilits, excepting thefirst pair, are broad and thin ( Fig. 228, A) and the tarsi arefringed with long hairs. \\hen swimming, the stroke ismade by the flat surface, aided by the spreading hairs; but onthe recover, the leg is turned so as to cut the water, whilethe hairs fall back against the tarsus from the resistance of thewater, as the leg is being drawn forward. The hind legs,being nearest the center of gravity, are of most use in swim-ming, though the second pair also are used for this purpose;indeed, a terrestrial insect, finding itself in the water, instinc-tively relies upon the third pair of legs for locomotion. Hy-drophilus uses its oar-like legs
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectentomology, bookyear1
