196 Wisconsin Academy of Sciences, Arts, and Letters, 
The specimens for use were easy to procure at certain times of 
the year, for during the summer and autumn months a sheet of 
paper left for a few days on one of the laboratory tables is sure to 
cover a number, large and small, but in the winter, beginning with 
November and continuing until May, the insects almost entirely 
disappear. Their favorite habitat is a dry and undisturbed place, 
and the tables of a laboratory, if dust-covered, suit them perfectly. 
It is useless to search for them on a clean table, even though it has 
been well sheltered by papers or books. Books infrequently used, 
or herbarium shelves, or dried grains packed away in boxes re¬ 
mote from sunlight are favorable habitats for them. As has often 
been noted in descriptions, the femur of the posterior pair of legs 
of Troctes is greatly enlarged, a characteristic of jumping insects, 
but observers have claimed this to be of no use to the animal. How¬ 
ever, in escaping from the collector, as they probably do in eluding 
animals which prey upon them, they put this feature to good use 
by making leaps backward before fleeing swiftly into some dark 
crevice. Before they can hide, they are easily picked up with a 
moist brush and dropped into hot water. 
Mouthparts 
The structure of the head and mouthparts of the Corrodentia has 
been of more interest to entomologists, particularly systematists, 
than any other feature of the anatomy of these insects, because of 
the similarity shown by them to corresponding parts of the Mal- 
lophaga. The oesophageal sclerite or ‘‘bonnet,” the so-called max¬ 
illary fork, and the chitinous structures of the labium known as the 
lingual glands are similar, to a striking degree, in the two orders. 
The first work which revealed to any extent the structure of the 
mouthparts of a form similar to Troctes was that of Burgess (5) 
in 1878 on the anatomy of the head in the Psocidae. In this he 
figured in detail some portions of the head and mouthparts of 
Psocus, with a few references to those of Troctes (called by him 
Atropos). Since his time the studies which have been made on 
these insects have been largely to determine the nature of the 
“lingual glands” and maxillary fork. Doubt has been expressed 
as to the glandular nature of the labial structures by Bertkau (4), 
Cummings (8) and Enderlein (10), and the true relationship of 
the maxillary fork is unknown. Is it an independent organ, not 
