Annual report of the Board of Regents of the Smithsonian Institution . y be in theregion of the body supporting the glider lobes;the second, that the creature must have theability to project itself into the air. We woulddraw the inference, therefore, that insectsequipped with glider lobes, if the lobes wereconfined to the thorax, had slender abdomensand carried the weight of their viscera moreevenly distributed in the body than do manyof the more specialized insects of the presenttime, and furthermore, that the gliding in-sects had well-developed legs which enabled them to run swiftly offthe e
Annual report of the Board of Regents of the Smithsonian Institution . y be in theregion of the body supporting the glider lobes;the second, that the creature must have theability to project itself into the air. We woulddraw the inference, therefore, that insectsequipped with glider lobes, if the lobes wereconfined to the thorax, had slender abdomensand carried the weight of their viscera moreevenly distributed in the body than do manyof the more specialized insects of the presenttime, and furthermore, that the gliding in-sects had well-developed legs which enabled them to run swiftly offthe end of a support, or to launch themselves into the air by avigorous leap. Many of the modern grasshoppers do not departfar from this primitive mode of fiight, except in that they combinean excellent pair of saltatorial legs with a pair of expansive sails thatcan perform also, in a weak manner, as organs of true flight. The ques-tion always arises, or is deliberately brought up to embar-rass every speculation in evolution, as to how organs could have been82322—3U 26. FiGUEE 4.—Outline of a modethat can be made, when prop-erly ballasted, to show some-thing of the possibilities of aglider insect 388 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1929 evolved in their earlier stages when they were too small to serve anyspecific function; and if we can not answer this question it is taken toinvalidate the assumption imphed by the theory. Certainly, para-notal lobes on the thorax could not have had any locomotory functionuntil they were large enough to serve as gliders. And yet, manymodern insects have lateral extensions of the back plate of theprothorax, such as occur frequently in the beetles, which appear tobe of no particular use to their possessors, and in some species ofmantids the back plate of the prothorax is expanded into a large, flatshield. (Fig. 5.) Utility probably guides the course of an organsevolution, but it does not necessarily determine its inception. Speci-fic structu
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