1915] The Head and Mouth-Parts of Thysanoptera 43 
for the long maxillary sete to function if they retained their 
connection with the reduced maxillary sclerites. However, 
their connection with the maxillary sclerites is not entirely 
lost since the thickenings from which the maxillary pillars 
(mx. p.) arise, extend to the tentorium (x. and z.), which is 
adjacent to the maxillary sclerites. These thickenings are 
undoubtedly derived from the tentorium, and since the maxille 
are associated with them they are possibly modifications of 
the posterior arms (p. a.). 
Muir and Kershaw in their work on a species of Tubulifera 
interpret the paired, piercing organs as mandibles. They 
give two lines of evidence. In the first place, they show that 
the asymmetrical piercing organ (1. md.) is a part of the 
maxilla, consequently the paired piercing organs must be man- 
dibles. Also they have proved to their own satisfaction by 
comparison with Rhynchota that the paired piercing organs 
are mandibles. ‘‘The paired sete we consider as mandibles, 
homologous to those of Rhynchota.” The first part of their 
evidence will be considered later. In regard to their own 
statement here quoted there is considerable doubt. They 
present no satisfactory evidence on this point, and as far as 
observed, the relations existing in Cicada permit of no such 
interpretation, as has already been shown. Jordan also studied 
individuals of the Tubulifera and came to the same conclusions 
as in his studies on the Terebrantia. The different inter- 
pretations of the paired piercing organs in the Thysanoptera 
of the authors mentioned above has been largely due to an 
incomplete comparative study of the nymphal and adult stages 
of both the suborders. 
MANDIBLES.—A large, heavy, unpaired piercing organ 
(1. md.) is present on the left side of the mouth-cone of all 
thrips (fig. 2, 3, 11, 12, 18, 22, 27, 28, and 33) while on the right 
side no such organ isfound. Berlese figures the asymmetrical 
piercing organ as occurring on the right side. Undoubtedly 
this is a mistake for in no case has such an occurrence been 
recorded by other workers. This asymmetry of mouth-parts 
is unique among insects. The asymmetrical, piercing organ 
connects with the head-capsule at the point where the left 
margin of the clypeus or the right margin of the maxillary 
sclerite comes in contact with the front. It is composed of 
