1915} The Head and Mouth-Parts of T. hysanoptera 55 
The small mass on the left side (fig. 26) projects for a short 
distance into the hollow cavity of the left mandible. This 
is not the case with the mass adjacent to the right, rudimentary 
mandible. These two small masses are connected with the 
masses above described by means of fine ducts (dus). The 
exact extent of these ducts has not been definitely determined. 
It is possible that they unite with the ducts entering the pharynx. 
It is also possible that the secretions from the small mass within 
the left mandible passes out thru the minute lumen of the 
mandible. In the concave portion of the labrum small masses 
of tissue are present which resemble the above so-called gland- 
ular tissue. The extent of these masses varies and as yet no 
ducts have been observed in connection with them. 
In Cephalothrips (fig. 48, 49-51, 55 and 59) the above sup- 
posed glandular tissue of the head is present but it is not so exten- 
sive. Two distinct masses can be identified cephalad of the 
pharynx and these give rise to ducts (d.) that empty into the 
pharynx as in Heliothrips. Also a small mass of similar tissue 
is located at the base of the left mandible but no such mass 
is found on the right side near the right mandible. No glandu- 
lar tissue was found in the concave portion of the labium as 
in Heliothrips. 
SUMMARY. 
1. The general arrangement of the head and mouth-parts 
of the Thysanoptera and the Hemiptera is similar. 
2. The resemblance between the mouth-parts of Thysan- 
optera and Orthoptera is apparently closer than the resemblance 
between the mouth-parts of Hemiptera and Orthoptera. 
3. A comparison of the different structures of the two 
suborders shows clearly that the suborder Terebrantia is more 
generalized than the suborder Tubulifera. 
4. The mouth-parts of thrips are fitted for sucking. 
0. The parts of the mouth are in the form of a cone which 
encloses the piercing organs. The cone is composed of the 
clypeus (cl.) labrum (Ir.), maxillary sclerites (mx. s.) and labium 
(is.). 
6. The mouth-parts of thrips are asymmetrical. 
7. The asymmetry of the clypeus (cl.) and the maxillary 
sclerites (mx. s.) in the two suborders is of an entirely different 
nature. 
