1915] The Head and Mouth-Parts of Thysanoptera 45 
The invaginations of the anterior arms of the tentorium (i. a.) 
in thrips are always located on the caudal margin of the front 
and adjacent to the asymmetrical piercing organ and the above- 
described piece. This evidence undoubtedly shows that this 
rudimentary piece on the right side is homologous with the 
asymmetrical piercing organ on the left. 
Helhiothrips femoralis (fig. 2, 5, 12, 19, 27 and 28.).—The 
left asymmetrical piercing organ and its right homologous 
rudiment are typical of the suborder Terebrantia and correspond 
to the general description given above. These parts in the 
nymph and adult closely resemble each other. In the nymph 
(fig. 28) the left, piercing organ is smaller, straighter, and its 
two halves less differentiated than in the adult (fig. 27). The 
basal half of the left, piercing organ is connected with the front 
by a narrow, chitinized neck. This connection is readily seen 
in frontal sections of the adult and nymph. 
The right, rudimentary piece in the nymph and adult 
extends as a distinct piece between the right cephalo-lateral 
margin of the pharynx and the front. This piece is homologous 
with the asymmetrical piercing organ (1. md.) and resembles 
somewhat its basal half. The distinguishing differences in these 
two are their size and the union of the right piece with the 
pharynx. Jordan represents a prominent projection on the 
right margin of the pharynx of Heliothrips hamorrhoidalis. 
This probably represents the asymmetrical piece above de- 
scribed. Garman found in his work on Limothrips a small, 
right, asymmetrical structure which he considered to be a 
rudimentary piece homologous with the left, piercing organ. 
These two pieces Garman designated as mandibles. This 
interpretation agrees with my own observations. Garman’s 
own words are, “The organ has every appearance of being a 
mandible. Its form and its relation to the other mouth- 
parts and to the epicranium all indicate this. Nothing cor- 
responding to this conspicuous organ is apparent on the right 
side of the head unless a very small, chitinous structure under 
the edge of the clypeus is a rudiment of the organ for this side.”’ 
Garman records the structure of the left mandible as con- 
sisting of one solid piece. The writer however, considers the 
left mandible as composed of two parts. At least in all thrips 
examined a distinct constriction occurs between the distal 
spine and the large proximal portion, and to all appearances a 
