Page:Popular Science Monthly Volume 39.djvu/241

Rh The maxillary palpi include from one to six pieces or joints. The labial palpi have from two to four. The intermediate piece, or tongue, is subject to great modifications. With the chin, it completes the buccal pieces.

In the licking and sucking insects the organs we have described are adapted to their new functions. Thus the tongue in bees reaches a great development; bugs, grasshoppers (Fig. 9), and lice have a long beak enveloping silky hairs, which form rudiments of jaws; in the butterflies we perceive a disproportionately



long proboscis; while in the Diptera the dispositions vary with the different groups. But in all these transformations the attentive observer will be able to perceive vestiges of the pieces comprising the mouth of the masticating insect which we have chosen as a type. These homologies were clearly established by De Savigny in 1816.

The eye and the head in vertebrates are movable. The visual rays consequently embrace a large horizon. The eye of the insect, on the contrary, is immovable, and solidly incased in the head; and the movements of the head itself are very limited. A great inferiority would result from this, had not Nature compensated for it by augmenting the circle of action of the eye itself. The insect's eye is formed by the union into a single mass of a considerable number of little eyes—sometimes exceeding twenty thousand (Fig. 11). Each of these minute organs, which are easily distinguished with a glass, comprises a hexagonal facet, representing the cornea; below this, a conical refracting mass represents the crystalline lens, and upon this abuts the nervous net emerging from the ganglion, which is itself in relation with the cerebral mass. The apparent part of the eyes is rounded, like a spherical cap, or rather like a portion of an ellipsoid. Sometimes the inner