A text-book of entomology, including the anatomy, physiology, embryology and metamorphoses of insects, for use in agricultural and technical schools and colleges as well as by the working entomologist . n length, these wing-coversare laid over on the back. However,if we study the process of development ofthe wings with a microscope, by meansof sections made obliquely through theFIG. 152. —Rudimentary wine of youns thorax, the process appears still morenymph of Blatta, with the five principal veins simple. The chief force of all evolution is and remains the power of growth in a definite directi
A text-book of entomology, including the anatomy, physiology, embryology and metamorphoses of insects, for use in agricultural and technical schools and colleges as well as by the working entomologist . n length, these wing-coversare laid over on the back. However,if we study the process of development ofthe wings with a microscope, by meansof sections made obliquely through theFIG. 152. —Rudimentary wine of youns thorax, the process appears still morenymph of Blatta, with the five principal veins simple. The chief force of all evolution is and remains the power of growth in a definite direction. In regard to the skin this growth is possible in insectsonly in this way ; namely, that the outer layer of cells is increased by the foldswhich are forced into the superficial chitinous skin. These folds naturally growfrom out- moult to another in proportion to the multiplication of the cells, andare not smoothed out until after the moulting, when the outer resistance is over-come. 1 ZurEntwiekelungsgeschichte uinl Reproductionsfahigkeit der Orthopteren. VonVitus Graber. Sit/imgsfoerichte <1. Classe der Akad. d. Wisseusch.,Wien. Bd. Iv, Abth. i, 1807 ; also Die THE PRIMITIVE ORIGIN OF THE WINGS 139 As. however, the first wing-layers depend upon the wrinkling of the generalintegument of the body through the increase in the upper layer, the furthergrowth of the wings depends in the later stages upon the wrinkling of the epi-dermis of the wing-membrane even, which fact we also observe under themicroscope when the new wings drawn forth from the old covers appear at
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishe, booksubjectinsects
