H. M. rARSHLEY 
3 
the lon< 2 ; inandibular and luaxillary setae, which, coiled in a ver 
tieal, double spiral, occupy the space thus provided. The same 
remarkable structiu'e in Arddus quadrilincatus, .1. robudus, and 
.1. siniilis (Aradinac) was discovered independently by Miss 
(diroline A. Ilosford, during; a morpholo«;ical investigation car- 
ried on in this lal)oratory. The occurrence of such an impor- 
tant and iieculiar type of structure in l:)oth groups is, in my opin- 
ion, convincing evidence that the Aradinae and Alezirinae are 
homophyletic, properly subordinate branches of a single well- 
defined family; and thus their other common characteristics can- 
not be viewed as merely adaptive features, due to convergent 
evolution in the same environment, as Reuter maintains, but 
must be held to signify close relationship. 
Habits 
The ethology of these insects, while very imiierfectly known, 
has certain interesting asiiects which would seem well worthy 
of closer investigation. Observations which have been made on 
two or three sjiecies indicate that they feeil on the juices of fungi, 
and it is likely that this will prove to be the general rule (with 
some exceptions, vide ci)inanto>nei(f<, p. 95), lint present know- 
ledge is insufficient to show whether or not the various species 
are restricted to definite sjiecies of fungi, or to the fungi aflecting 
particular trees, as is suggested liy such facts as the constant 
occurrence of stmilis, for instance, about Folyporus betulinus, 
the shelf-fungus of birch. 
There are some indications of nascent social instincts to l)e 
observed in the behavior of many of the species, for very com- 
monly little colonies made up at most seasons of adults and 
young in various stages of develo])nient may be found clustered 
in small areas, even where a consideralile expanse of apparently 
uniform conditions is afforded by large sheets of bark. 
In their flattened form and in the peculiar mode of articula- 
tion of their appendages, the Aradids display structural features 
most admiralily suited to their peculiar abode, which bring to 
mind very forcil)ly the vexed questions of adaptation. Ages 
ago, some more or less flattened ancestor, under the influence, 
perhaps, of a newly-acquireil negative phototropism, discovered 
TK.VNS. AM. ENT. SOC,, XLVII. 
