1915] The Head and Mouth-Parts of Thysanoptera 29 
of the facets when they have been treated with potassium 
hydroxide. In the adult of Cephalothrips the eyes do not 
protrude from the head-capsule, the facets are numerous, 
clear, and all approximately of the same size. 
OcELLI.—The ocelli as far as observed are three in number. 
They are situated on the dorsal aspect of the head between the 
compound eyes in the form of a triangle with the median ocellus 
on the cephalic side. In the two species figured the ocelli of 
Heliothrips (fig. 7) are clear oval bodies located on a small, 
elevated, triangular area, while the ocelli of Cephalothrips 
(fig. 9) are clear, circular bodies, larger than the facets of the 
compound eyes, more distant from each other than those of 
Heliothrips and not elevated above the general plane of the 
head-capsule. No traces of ocelli were found in the nymphs. 
TENTORIUM OR INTERNAL HEAD-SKELETON.—Under this 
heading only those internal structures found in the head that 
pertain to the tentorium will be considered. For other internal 
parts the discussions on the maxillae, pharynx and salivary 
glands should be consulted. 
One finds within the head of a generalized insect a definite 
arrangement of rod- and plate-like structures which go to 
‘support the internal organs and furnish points of attachment 
for muscles. . These rods or plates extend from three pairs 
of openings on the head-capsule. These openings are known 
as the invaginations of the anterior arms, dorsal arms and 
posterior arms of the tentorium. The invaginations of the 
anterior arms are usually associated with the lateral margins 
of the clypeus and with one of the points of articulation of the 
mandibles. The invaginations of the dorsal arms are associated 
with the points of attachment of the antennae. The invagi- 
nations of the posterior arms are associated with the occipital 
foramen, and the point of attachment of the maxillae. These 
generalized relations become modified in the various orders 
and families of insects. The invaginations may disappear and the 
rods and plates undergo striking changes or become atrophied. 
The important point, however, is that in all orders of insects, 
so far as observed, the invaginations and the arms of the tent- 
orium are always associated with the appendages named. 
These associations exist in thrips and an attempt will be made 
to show that they have an important bearing on the homology 
of their mouth-parts. 
