1927] 
Olfactory Function of the Antennae of Insects 
209 
EVIDENCE IN SUPPORT OF THE OLFACTORY 
FUNCTION OF THE ANTENNAE OF INSECTS. 1 
By R. W. Glaser 
1. The Present Status of the Problem. 
Investigators agree that chemotropism or the reaction of an 
animal to chemical stimuli plays a very important role in the 
biology of insects. Richardson (1) recently reviewed the ex- 
tensive literature on odor as a factor in the selection of places for 
oviposition and in the choice of food. Odor likewise assists 
insects in gathering material for their nests, in detecting mem- 
bers of their own or “alien” species, and in bringing the sexes 
together. 
The assignment of the sense of smell to particular organs has 
been beset with great difficulties. Most histologists assign the 
olfactory sense chiefly to the antennae. On these organs sensillae 
are found in the form of pits, cones or plate organs which are 
morphologically of such a nature that a chemoreceptor function 
has been attributed to them. Similar sensillae may occur in other 
places, as on the maxillary and labial palpi, on the cerci and 
perhaps elsewhere, but they seem generally to be numerically 
greatest on the antennae. Correlations between the number of 
antennal sensillae and the habits of certain insects have disclosed 
a number of facts. The antennae of Diptera that oviposit on 
putrid meat or feces harbor many olfactory pits whereas phyto- 
phagous forms possess few. Bloodsucking flies have many, as do 
those forms whose larvae are parasitic, such as Oestrids, Bomby- 
liids and Tachinids. The Hymenoptera possess enormous 
numbers of antennal sense organs. In male honey bees the 
number of plate organs has been computed at 30,000. In Odo- 
nata, large-eyed forms that prey on other swiftly moving insects, 
the number of antennal olfactory sense organs is small. Among 
those species where sexual dimorphism of the antennae exists, 
these organs are generally more fully developed in the males 
than in the females. This seems to be associated with the more 
Trom the Department of Animal Pathology of the Rockefeller for 
Medical Research, Princeton, N. J. 
