Nettling Insects 
5i 
through the cuticula for each individual hair, there is a single pore 
for each papillae on a tubercle, all the hairs of the papilla being 
connected with the 
underlying cells 
through the same 
pore canal, (figs. 
39 and 40). 
The hypodermis 
of this region is of 
two distinct types 
of cells. First, 
there is a group of 
slender fusiform 
cells, one for each 
poison hair on the 
papilla, which are 
the trichogen, or 
hair-formative cells. They are crowded to one side and towards 
the basement membrane by a series of much larger, and more promi¬ 
nent cells (fig. 40), of which there is a single one for each papilla. 
These larger cells have a granular protoplasm with large nuclei and 
are obviously actively secreting. They are so characteristic in 
appearance as to leave no question but that they are the true 
poison glands. 
Poisonous larvae of many other species have been reported from 
Europe and especially from the tropics but the above-mentioned 
species are the more important of those occurring in the United States 
and will serve as types. It should be noted in this connection that 
38. Cross section of the larva of the browntail moth showing the 
tubercles bearing the poison hairs. Drawing by Miss 
Kephart. 
39. Epithelium underlying poison hairs of the larva of the 
browntail moth. Drawing by Miss Kephart. 
