1915] The Head and Mouth-Parts of Thysanoptera 47 
Cephalothrips yucce (fig. 11, 18, 22, 26, 33, 34, 35 and 36).—A 
striking similarity exists between the ental view of the mouth- 
parts of anymph of Cephalothrips (fig. 22) and the adult stage 
of Heliothrips (fig. 27). This similarity is particularly notice- 
able in respect to the structure and position of the asymmetrical 
piercing parts. On the basis of this similarity it is possible 
to derive the correct interpretation of the asymmetrical, 
piercing organs. The left mandible (1. md.) in the nymph is 
a long, nearly straight, stout, two-segmented structure and con- 
nects with the caudal margin of the front (f.) at the point where 
the maxillary sclerite and clypeus unite with the head-capsule. 
Between this point of connection and the invagination of the 
left dorsal arm of the tentorium a thickening occurs (a. a.). 
This thickening is the anterior arm of the tentorium and can be 
seen in carefully stained and dissected material. 
The right, rudimentary mandible in the nymph of Cephal- 
othrips is represented by a distinct chitinized thickening be- 
tween the clypeus and the right maxillary sclerite. The 
distal end of this thickening (r. md.) unites with the right 
lateral margin of the pharynx as seen in cross-sections of the 
adult pharynx (fig. 55 and 56). Figures 33 and 35 do not 
show this connection because of the spreading of the heads. 
The above nymphal evidence clearly demonstrates the 
homology between the asymmetrical mandibular parts of a 
species of Tubulifera and those of a species of Terebrantia. 
The evidence used in proving that the asymmetrical piercing 
organs of the Terebrantia are mandibles is equally applicable 
in demonstrating that the asymmetrical parts in the Tubulifera 
are also mandibles. One exception however occurs in the fact 
that in the nymph of Cephalothrips the invaginations for the 
anterior arms have not been identified along with other ten- 
torial structures. 
The mandibular parts of the adult (fig. 33) undergo a 
distinct modification due to the reduction in the size of the 
mouth-cone. In this change the left mandible (1. md.) retains 
its position between the clypeus and the left maxillary sclerite, 
but in so doing the heavy, proximal portion turns and forms 
a half circle. This modification has resulted in the forniation 
of a distinct notch (n.) in the clypeus and the left maxillary 
sclerite. It has also resulted in the uniting of the meso-cephalic 
