270 Sense of Smell in Insects . [May, 
has crept. All these phenomena are rationally expli- 
cable if the antennae are the organs of scent. They 
are utterly unintelligible if we suppose them to be 
organs of hearing or touch. On the other hand, it 
has not been shown that Dr. Wolff’s organ has any 
exceptional development in the males of Saturnia , &c., 
either as compared* with their respective females or 
with other species where the locomotive powers of the 
sexes are nearly equal, and where consequently the 
males require no exceptional faculties for seeking their 
mates. 
We take the next case, — the relatively greater develop- 
ment of the antennae in noCturnal groups, with which we 
may couple the inverse perfection of these organs as com- 
pared with the eyes. It will be admitted that if the antennae 
are the organs of smell, this difference is precisely what 
might be expected. Species whose sight is exceptionally 
acute and powerful, and who in addition, like the dragonfly 
and the house-fly, are swift and enduring on the wing, have 
relatively little need of complicated scent organs. Con- 
versely those which are slow in their walk and flight, such 
as the clumsy dung-beetles, and whose eyes g are in comparison 
small or less advantageously situate, require an acute scent 
to compensate for the deficiency. It is very doubtful whether 
an enemy or a booty to be captured could approach a dragon- 
fly from above, below, or behind without being detected. 
But, e.g., the Dynastidse may be approached from behind, 
from above, and to some extent from the sides, without 
coming within their range of vision. Here, therefore, espe- 
cial delicacy of scent must be needed, or must at least be 
beneficial to such species as possess it. It may, then, be 
fairly submitted that the nicety of the sense which they need 
will be causally connected with the organs which in them are 
so signally developed. 
We turn next to the distinction between the monophagous 
and the polyphagous groups and species. It can require no 
formal demonstration that the former must require more 
accurate means of seeking their nutriment than the latter. 
The blowfly, which loves carrion, but which in case of need 
does not object to the neCtar of flowers, the juices of fruits, 
and the excreta of animals, is in little danger of starvation, 
and its sense of smell does not require to be finely discrimi- 
nating. On the other hand, the sexton-beetle (N ecrophorus ) , 
which feeds on small carrion, and nothing else ; the Geo- 
trupes , which preys on the excreta of the herbivorous animals, 
