1915] The Head and Mouth-Parts of Thysanoptera 35 
ANTENNAE (fig. 4).—The antennae of the adult of Helio- 
thrips are about twice the length of the head-capsule, eight- 
segmented and reticulated with chitinous elevations cor- 
responding to the reticulations (rt.) on the head-capsule. 
The shape, size, reticulated character and the setal arrangement 
are shown in the figure. Segments one, two, six, seven and 
eight are of a brownish color similar to the head-capsule while 
the remaining segments are but slightly pigmented. The 
distal end of segment four gives rise to a thin, hyaline, two- 
branched sense cone (s. c.). The sense cones are not present 
in the antennae of the nymph. Except for this the antennae 
of the nymph are structurally similar to those of the adult. 
The antennae of the nymph and adult of Cephalothrips 
resemble each other and are of the same number of segments, 
eight, providing the very small pieces at the distal ends of the 
nymphal antennae are considered as segments. In the first 
stages of the semi-pupa (fig. 20) the antennae appear as 
mere buds at the cephalic margin of the head-capsule. As the 
insect becomes older, the antennal cases increase in size and 
length until they extend around the lateral margins of the head- 
capsule. A late stage of. the semi-pupal instar shows seg- 
mentation on the distal portions of the antennal cases. The 
eight-segmented antennae of the adult are about one and one- 
third times longer than the dorsal aspect of the head-capsule 
and have a yellow color thruout, except the two basal segments, 
which are of a brown tinge. The general shape, size and setal 
arrangement of the segments is shown in figure 10. Segments 
three, four, five and six each possess at their distal end a pair 
of simple, hyaline, spine-like sense cones (s. c.). The sense 
cones are wanting in the nymph. 
LABIUM.—The mouth-parts of Hemiptera are fitted for 
sucking. In this adaptation the labium is modified into a long, 
trough-like beak, enclosing the bristle-like mandibles and 
maxillae. The mouth-parts of Thysanoptera are also fitted 
for sucking. The adaptation in thrips, however, is not confined 
to the specialization of one part of the mouth, but the clypeus, 
labrum, maxillary sclerites and labium together form a broad 
and blunt mouth-cone, enclosing the needle-like mandibles 
and maxillae. Of these two types of sucking mouth-parts, 
those of the Thysanoptera more closely resemble a generalized 
