120 
Wisconsin Academy of Sciences , Arts and Letters. 
[ ’86] has described the formic acid secretion ejected from the prothorax of 
Dicranitra vinula. According to the same observer Dicranuro, fur cat a 
everts from the same region of the prothorax a gland “ consisting of six 
diverging processes of a light green color, divided into two groups of three 
each.” He also mentions an eversible gland in the prothorax of the 
larvae of Melitaea artemis and Catocala species. 
Peculiar scent organs, resembling those of the larval Papilio and con¬ 
sisting of a pair of tentaculiform processes, eversible from between the 
seventh and eighth ventral segments of the male imagines, have been des¬ 
cribed by Smith (’86) for the Bombycids Leucarctia acrcea and Pyrrharctia 
Isabella. These processes, which are orange colored and fully half an inch 
long in Leucarctia, but whitish and somewhat shorter in Pyrrharctia are 
covered with hairs, blackish in the former and snow white in the latter 
species. “In both species an intense odor, somewhat like the smell of 
laudanum, is apparent when first the tentacles are exposed; and there is 
no reasonable doubt but that they are odor-glands, though exactly what 
purpose they serve is not so clear.” Smith says that a Mr. Morgan has 
described these organs in L. acrcea and similar structures in Agrotisplecta 
and Euplexia lucipara; and that similar organs have been described for 
Aletia xylina by Riley. 
Among the Diptera prominent cases are rare. Coenomyia ferruginea 
emits an odor which reminds me of the juice of a certain species of 
Hypericum, and which has often enabled me to detect the presence of the 
insect in the woods when several feet distant. The odor is retained in 
dried insects that have preserved for years in collections. The species of 
Gastrophilus have a sharp, disagreeable smell, powerful in some species, 
faint, but still perceptible in others. ( Leunis ’86, vol. II. p. 419.) 
Among the Hymenoptera the formic acid secretions of the ants are well 
known. The catapillar-like larvae of the species of Cimbex, both Eu¬ 
ropean and American, when irritated secrete a pungent green liquid from 
pores arranged along the sides of the body. 
The cases cited are but a few of the many that will occur to every field 
entomologist. The histological structure of the glands, so different in 
different forms, has not been considered, as it would lead me beyond the 
confines of my subject. On a priori grounds we should expect to find that 
structures so useful to their possessors as the odorifferous glands are to in¬ 
sects, have been profoundly modified by the action of natural selection. 
Their wide occurrence in insects of all orders shows, moreover, that they 
have been in use for a great length of time. The Archentoma probably 
lived in damp places like those inhabited by the living species of Peripatus, 
Myriopoda, Thysanura and Blattidae and, being of a harmless nature like 
their modern descendants, might have made considerable use of large 
odoriferous glands on the pleurae. 
If I am correct in my supposition that the pleuropodia functured in the 
Archentoma as odoriferous organs, they must be regarded as much less per- 
