The opening of Letter XXXVII
_INTERNAL ANATOMY AND PHYSIOLOGY
OF INSECTS._SENSATION.
Having given you this full account of the external parts of insects, and their most remarkable variations; I must next direct your attention to such discoveries as have been made with regard to their Internal Anatomy and Physiology: a subject still more fertile, if possible, than the former in wonderful manifestations of the POWER, WISDOM and GOODNESS of the CREATOR.
The vital system of these little creatures, in all its great features, is perfectly analogous to that of the vertebrate animals. Sensation and perception are by the means of nerves and a common sensorium; the respiration of air is evident, being received and expelled by a particular apparatus; nutrition is effected through a stomach and intestines; the analogue of the blood prepared by these organs pervades every part of the body, and from it are secreted various peculiar substances; generation takes place, and an intercourse between the sexes, by means of appropriate organs; and lastly, motion is the result of the action of muscles.