2 
Psyche 
[ March 
For example, the concurrence of Trichoptera and Lepidop- 
tera is not questioned and some investigators have suggested 
that these two groups might even be conceived of as one 
valid order. The nature of the claw-segment of Astenophy- 
lax (Fig. 21) and Automeris (Fig. 22) shows at a glance 
the proximity of these structures even in such advanced re- 
presentatives of the respective orders. 
The relative value of a structure like the pretarsus as a 
phylogenetic guide may be uncertain, but the above example 
indicates that such consistency of the claw-segment from 
order to order should make it of considerable utility in 
checking theoretical relationships. Although the basic plan 
of the pretarsus presents a certain conformity throughout 
the orders, there are sclerites which are variable enough to 
warrant their investigation from the standpoint of taxon- 
omy. For example, within the Hymenoptera the orbicula 
may be important in this respect. Hayes and Kearns 
(1934) have studied the empodium of Coleoptera and find 
that the Adephaga is the only group showing any consis- 
tancy in structure; they conclude, in general, that there is 
in some a tendency towards generic or family uniformity 
but that the super-families are decidedly heterogeneous. 
Arolia and pseudarolia have long been used as the basis of 
classification for the Miridae and for other Hemiptera the 
empodium may prove to be of taxonomic value. 
Acknowledgements 
The writer is indebted to Professor C. T. Brues and Pro- 
fessor G. C. Crampton for their advice during the prepara- 
tion of this paper, and to them and to the Museum of Com- 
parative Zoology for much of the material herein figured. 
Terminology. 
The general structure of the pretarsus has been figured 
many times for different orders : Snodgrass gives detailed 
descriptions of the condition in the honey-bee (1925) and 
figures several other types (1927) ; Crampton (1923) com- 
pares the claw-segment of Periplaneta with those of Leptid 
and Asilid Diptera; Hayes and Kearns (1934) have studied 
the pretarsus of Coleoptera and summarize past work on 
