1915] The Head and Mouth-Parts of Thysanoptera 21 
extend from the proximal to the distal end of the wings in the 
Terebrantia, while only one, partially developed, median 
vein occurs in the Tubulifera. 
The Terebrantia are divided into two families, Aeolothripidae 
and Thripidae, while only one family, Phloeothripidae, occurs in 
the Tubulifera. It is generally stated by investigators in this 
field that the Terebrantia are the more generalized and of the 
two families in this suborder the Aeolothripidae are the more 
primitive. The following brief summary of the evidence as 
discussed by Uzel in his ‘“‘Monographie der Ordnung Thy- 
sanoptera,’’ page 22, supports the above statement. 
The wing characters of the Terebrantia are more generalized 
than those of the Tubulifera. The wings of the Terebrantia 
possess one or more complete longitudinal veins and in some 
cases cross veins, while the Tubulifera have only one partially 
developed longitudinal vein and no cross veins. Cross veins 
among the Terebrantia are present only in the family Aeo- 
lothripidae. The antennae of most Aeolothripidae are nine- 
segmented while in all other thrips except the genus Heter- 
othrips there are six to eight segments found. The maxillary 
palpi of the Aeolothripidae are four-segmented, while those of 
the Thripidae are usually three-segmented and those of the 
Phloeothripidae are composed of two long segments. The 
labial palpi of the Aeolothripidae are always four-segmented 
while those of other thrips have but two segments. The 
above data permit the assumption that the Terebrantia are 
more primitive than the Tubulifera. This assumption is 
substantiated by the comparative studies of the suborders 
made in this paper. 
The primary purpose of this research is to reach as definite 
a conclusion as possible in respect to the interpretation of the 
asymmetrical mouth-parts of the Thysanoptera. The litera- 
ture of this subject shows a decided diversity of views as to 
their homology and function. Some investigators consider 
the mouth-parts as fitted for biting, and others as fitted for 
sucking. The more recent workers, while agreeing that they 
are of a sucking type, yet disagree as to the homology of the 
mouth-parts. Besides the study of the mouth-parts, many 
interesting head structures have been observed. Of these the 
pharynx, salivary glands and head-glands are discussed and 
figured. 
