1887] Entomology. 183 
to have a distinct reference to the perception of odors.. It com- 
prises a structure composed of nervous substances which are 
enclosed in a chitinous tube, and either only stand in relation to 
the surrounding bodies by the perforated point, or pass to the 
surface as free nerve-fibrilla. 
Wolff’s theory that the sense of smell is lodged in the skin of 
the soft palate-like roof of the mouth is published in a work of 
two hundred and fifty quarto pages, which shows so much skill, 
acuteness, and subtle reasoning that his views prevailed for several 
years, and were adopted by Graber in his well-known work on in- 
sects. Forel appears to have been the first to oppose Wolff's con- 
clusions, both on theoretical grounds and from his experiments on 
Polistes and Sphex. Leydig, in his work on Amphipoda and Iso- 
poda (p. 235), expresses the view that “this nasal skin possesses 
nothing more special than other regions of the skin which should 
be considered as tactile.” I think that Leydig is here perfectly 
correct, and that those small pit-hairs are plainly tactile organs, 
since such must be present in the mouth near the organs of taste. 
Moreover, it is generally. doubtful whether such direct sense-per- 
they are formed to feel and repel solid bodies, rather than to 
smell them. The presence of a gland differing in the nature of 
its secretion from the other glands of the mouth, on which Wolff 
laid so great weight, should not have much force as an argument, 
` since we know as good as nothing of the chemistry of digestion 
and the secretions in insects necessary for it. The apparatus is 
better fitted by its situation for a gustatory apparatus. Hence we 
should adopt Leydig’s view of the tactile nature of these minute 
hairs so long as no further anatomical and physiological data 
prove their gustatory function. ; 
In insects there is a remarkable and fundamental difference in 
the structures of the parts supposed to be the organs of smell. 
Erichson (10) was acquainted only with the “pori” covered by 
a thin membrane; but Burmeister (11), in his careful work on the 
antennz of the lamellicorns, distinguished pits at the bottom of 
which hairs rise from a glass-like tubercle, from those which were 
_ free from hairs. Leydig (14) afterwards was the first to regard 
as olfactory organs the so-called pegs (kegel), a short, thick hair- 
like structure distinctly perforated at the tip, which had already 
by Lespés (38) in Cercopsis, etc., been described as a kind of 
tactile papilla. Other very peculiar olfactory organs of different 
form Forel (Fourmis de la Suisse) discovered in the antenne of 
ants, which Lubbock (“On some points,” etc.), according to a short 
Ee. 
