SENSATION IN INSECTS. 499 
ever, the case is very different. Kraepelin [278] says: ‘ The seat 
of smell has for a long time excited the interest of authors. An 
extensive literature has accumulated, and there is no subject, 
perhaps, in zoological knowledge which has been treated with 
more acumen, and in which so extensive a literature has pro- 
duced so small a result. Even to-day, in spite of the many 
investigations of the last decade, we are far from a complete 
solution of the subject.’ 
I think, however, Kraepelin’s masterly work, and the further 
researches which have followed it, more especially in relation 
to the structure of the antennal ganglia, justify the view that 
the antenne are the main agents of the olfactory sense. 
Tactile Sense.—The antenne are usually regarded as tactile 
organs, but this sense is also undoubtedly common to the 
larger setee, and perhaps to the integument generally. Osten- 
Sacken says of the Diptera: I assume, therefore, that the 
macrochete (large bristles) are organs of orientation, con- 
nected with the nervous system, being in their useful action 
not unlike the whiskers of a cat.’ 
I have already observed (p. 474) that the phenomena of reflex 
action, in a decapitated fly, show conclusively that the general 
integuments, horny as they are, possess a keen sensibility, and 
the persistent manner in which insects clean themselves, or in 
which Ants and other social insects lick each other, indicate 
that the integuments are sensitive. 
Sensations Peculiar to Insects.—It has been siegeeied by many 
that insects possess senses of which we are totally ignorant ; 
but it is by no means easy to understand what is meant by the 
suggestion. Johannes Miiller wrote: ‘ The essential attribute 
of a new sense is, not the perception of external objects or 
influences which do not act on the senses of man, but that 
external causes should excite a new and peculiar kind of 
sensation different from all the sensations of our five senses. 
The possibility of the possession of such a faculty, by some 
animals, cannot be denied. No facts, however, are known 
which establish the existence of such a new mode of sensa- 
tion’ [192]. 
