24 Annals Entomological Society of America [Vol. VIII, 
ACKNOWLEDGMENTS. 
This investigation was carried on under the supervision of 
Dr. A. D. MacGillivray and Dr. J. W. Folsom, and to these 
men I am greatly indebted for the sincere interest shown and 
the many valuable suggestions received. For the use of the data 
on the tentorial structures and their relations in insects in 
general referred to in this paper, I wish to express my thanks 
to Dr. A. D. MacGillivray, who allowed me the free use of his 
unpublished manuscript; and to Miss Margaret Washington for 
the loan of drawings of the tentorium. I am indebted to Mr. 
J. D. Hood, of the U.S. Biological Survey, for the identification 
of the following five species: Heliothrips femoralis Reuter, 
Frankliniella tritici Fitch, Thrips physapus Linn., Cepha- 
lothrips yucce Hinds, and Haplothrips verbasci Osborn; to 
Dr. A. F. Shull, of the University of Michigan, who kindly 
furnished several species of named thrips; Euthrips (= Franklin- 
iella) tritici Fitch, Thrips tabaci Lindeman, Chirothrips man- 
icatus Haliday and Anaphothrips striatus Osborn; to Professor 
H. Garman, who supplied me with a few specimens of Limoth- 
rips cerealium, the species he used in making his observations; 
to Dr. W. E. Hinds for identifications and information, and 
to Professor S. A. Forbes and Dr. J. S. Kingsley for corrections 
and suggestions. 
FIXED PARTS OF THE HEAD. 
In the order Thysanoptera the gross arrangement of the 
head and mouth-parts (fig. 1, 2, 5, 8, and 11.) is homologous 
with the corresponding arrangement of the head and mouth- 
parts of a generalized homopteron. The cone-like mouth- 
parts are attached to the caudo-ventral portion of the head- 
capsule and project caudad between the prothoracic legs, and 
the antennae are located at the extreme cephalic margin of 
the head between the compound eyes (fig. 1 and 8). 
HEAD-CAPSULE (fig. 1, 2, 5, 7, 8, 9, and 11).—Head structures 
in thrips differ in many respects from those of a generalized 
insect. In the head-capsule nearly all of the sclerites are com- 
pletely united and all traces of sutures have been lost. On 
account of this union the following areas of the head, front 
(fr.), vertex (vt.), genae (g.), and occiput (0.), are designated 
only in a general way on the figures. The labrum and the 
