588 THE SENSES AND SENSORY ORGANS 
between them—the so-called pore plates—of which each 
antenna has from 17,000 to 18,000. These are about 5 ™ in 
diameter (Fig. 72, E). 
Sections show that the pore-plates are the orifices of flask- 
shaped canals (Pl. XLI., Fig. 2, A). The canals are sur- 
mounted by transparent sensory sete, 50 # in length. These 
sensory sete are nearly straight; they are conical, and in 
many preparations exhibit the appearance of having a slit 
running down one side and ending toward the apex of the seta 
in an oblique opening. Each contains a process from a 
ganglion cell, which is partially embedded in the pore canal. 
These setz are very easily detached, and leave their contents 
projecting from the pore canal as a flame-shaped process—the 
olfactory cone of authors. Sometimes the term ‘olfactory 
cone’ has been applied, however, to the seta. In a few pre- 
parations I have observed a fine axis cylinder only projecting 
from the pore canal; but I believe, like the flame-shaped 
cones, this is only the result of the detachment of the seta 
from its base, the greater part of its contents having been torn 
away with the seta itself. All these conditions have been 
figured by Krapelin, who took them for modifications of a 
typical seta. 
The short, thick, opaque setee which spring directly from 
the epidermal cuticle are only about half as long as the sensory 
sete. Their function is probably to protect the bases of the 
sensory sete. 
The arrangement of the hypodermal and ganglionic cells 
beneath the cuticle will be readily understood by a reference 
to the figures (Pl. XLI., Figs. 1 and 2). 
The subcutaneous ganglion cells are the superficial layer 
of the terminal ganglion of the antennal nerve ; beneath these 
there are numerous layers of far smaller round cells, which 
form its deep layer. This ganglion consists of a continuous 
layer, 50 p or 60 pw thick, over the whole inner surface of the 
integument of the third joint of the antenna. Its cells are sup- 
ported and bound together bya fine reticular stroma. Some of 
the terminal branches of the nerve can be traced directly to 
