42 Annals Entomological Society of America [Vol. VIII, 
cephalic ends of the maxillary guides and at first are dorsad of 
the guides. In their caudo-ventral extension they pass along 
the lateral sides of the trough-like guides and laterad of the 
pharynx toward the tip of the mouth-cone beyond which the 
two distal, grooved, needle-like portions interlock and pro- 
ject as a single piercing organ (fig. 25). The maxillary guides 
show no relation to the tentorial structures of the head. 
The paired piercing organs (mx.) of Cephalothrips, except 
for size, and point of attachment in the adult, resemble the 
maxillary setze of Heliothrips. The linear extension of the 
maxillary sete in Cephalothrips is due largely to the increased 
length of the distal and proximal pieces. The large proximal 
piece in the adult possesses a distinct knob on its mesal margin 
which serves as a point of attachment for muscles. The 
resemblance between the maxillary sete in the nymph or adult 
of Heliothrips (fig. 27 or 28) and the paired piercing organs in 
the nymph of Cephalothrips is very striking and important. 
The feature of significance in the nymph of Cephalothrips is the 
point of attachment of the paired piercing organs with the 
cephalic margin of the maxillary sclerites. This shows clearly 
that the paired piercing organs of Cephalothrips are not only 
homologous in structure but in point of articulation with the 
maxillary sete of the Terebrantia. The paired piercing organs 
of the Tubulifera are therefore maxillary sete. -The evidence 
used to prove that the paired piercing organs of the Tere- 
brantia are maxillary in origin will likewise hold for the Tu- 
bulifera with the exception of the evidence based on the ten- 
torium, since some of the tentorial structures are wanting 
in the nymph of Cephalothrips. 
The relation of the maxillary sete to the mouth-parts in 
the adults of the Tubulifera (fig. 33) is apparently very different 
from the conditions found in the Terebrantia. The reduction 
of the mouth-cone explains to a large extent the characteristic 
modifications of this suborder. In the reduction of the mouth- 
cone the proximal pieces of the long maxillary sete (mx.) do 
not retain their point of articulation with the maxillary scler- 
ites but articulate in acetabula located in special elevated 
maxillary pillars (mx. p.) on the ental surface of the head- 
capsule cephalad of the maxillary sclerites. This modification 
is a result of a mechanical necessity. It would be impossible 
