34 Annals Entomological Society of America |Vol. VIII, 
A distinct strip (st.) is present on the caudal margin of the 
head-capsule of Cephalothrips and extends between the short 
sutures (s.) which arise from the latero-caudal margin. Stained 
material shows clearly that this area (st.) is structurally dif- 
ferent from the head-capsule cephalad of it. On the ends 
of this area (st.) two depressions are present which are similar 
in many respects to the invaginations of the tentorium. If 
these are invaginations of the posterior arms then this is a 
thickening composed of the union of the posterior arms about 
the dorsal margin of the occipital foramen. This interpretation — 
is rather questionable since no invaginations of the posterior 
arms have been seen in the more generalized thrips. 
As a conclusion to the above discussion on the internal 
head-skeleton, the following statements are of importance. 
The tentorium and the associated mouth-parts of an homopteron 
such as Cicada can be interpreted on comparison with the same 
parts in a generalized insect. The arms of the tentorium and 
their respective invaginations in the nymph of one of the 
Terebrantia can be homologized with the tentorial parts of a 
Cicada. On the basis of this homology the specialized and 
atrophied conditions existing in the adults of the Terebrantia 
and in the nymphs and adults of the Tubulifera can be inter- 
preted. 
Furthermore, on the basis of this homology between the 
tentorium of thrips and other insects an attempt will be made 
to demonstrate the association of the mandibles and the 
maxillae with their respective tentorial parts. This should 
give conclusive evidence as to the correct interpretation of 
the two sets of piercing organs. See discussion on mandibles 
and maxillae for this demonstration. 
MOVABLE PARTS OF THE HEAD. 
The movable parts of the head will be considered in the 
following order: antennae, labium, maxillae and mandibles. 
In the discussion of the movable appendages those of the 
generalized Terebrantia will be considered first and then the 
homologous structures of the Tubulifera will be compared 
with them. 
