Morphological Studies on the Head and Mouth-Parts of the Thysanoptera.*

The small insects of the order Thysanoptera have four long, narrow, membranous, flat, fringed wings. Only a few veins are present in the wings and when at rest they are laid horizontally along the back. The sucking mouth-parts form a cone at the caudo-ventral margin of the head-capsule. The maxillae, in part, and the left mandible are modified into piercing organs and enclosed within the mouth-cone. The mandibles, clypeus and maxillary sclerites are asymmetrical. The tarsi are two-jointed, bladder-like at the distal end and without claws. The metamorphosis is incomplete.