. Animal and vegetable physiology considered with reference to natural theology. Natural theology; Physiology; Plant physiology; Biology. AQUATIC INSECTS. 301 to very large haunches, for the purpose of contain- ing the thick muscular bands which are inserted into the trochanter, and by which these joints are moved with great power. As the motion of these oars is to be performed in a plane nearly parallel to the axis of the body, the haunches are not re- quired to be moveable: and accordingly they are firmly united to the thorax; a structure which ren- ders the motion of the other joints more r
. Animal and vegetable physiology considered with reference to natural theology. Natural theology; Physiology; Plant physiology; Biology. AQUATIC INSECTS. 301 to very large haunches, for the purpose of contain- ing the thick muscular bands which are inserted into the trochanter, and by which these joints are moved with great power. As the motion of these oars is to be performed in a plane nearly parallel to the axis of the body, the haunches are not re- quired to be moveable: and accordingly they are firmly united to the thorax; a structure which ren- ders the motion of the other joints more regular and uniform. When the Dytiscus wishes to rise, it need only desist from all action, and abandon itself to the buoyant force of the fluid, which quickly carries it to the surface. Among the Hemiptera, the Notonecta, or water- boatman (Fig. 158,) is remarkable for always swim- ming on its back, a peculiarity depending on the form of its body, which is semi-cylindrical, with the legs affixed to the flat surface; so that, when lying on its back in the fluid, the centre of gravity is below the centre of the whole figure, (or the metacentre, as it is termed,) and the equili- brium is maintained. It is evident that, under these circumstances, if it were placed in the water with its legs undermost, it would unavoidably tilt over, and resume its usual position. Its long legs, extending at riglit angles to the body, present a striking resemblance to the oars of a boat; they act, indeed, in the same manner, and on the same Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Roget, Peter Mark, 1779-1869. London : W. Pickering
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