THE OLFACTORY ORGANS OF DIPTERA 483 
pores found in the four orders examined varies as follows: For 
Hymenoptera, from 463 to 2608 with 1286 pores as an average; 
for Lepidoptera, from 514 to 1422 with 850 pores as an average; 
for Diptera, from 473 to 1550 with 772 as an average; and for 
Coleoptera, from 273 to 1268 with 724 pores as an average. 
As in Lepidoptera, the olfactory pores of Diptera are dome- 
shaped and their internal anatomy is very similar to that of those 
in the other three orders, but the sense cells in the halteres are 
more spherical than usual. 
For description the pores have been divided into four types as 
follows: The Hicks’ type includes all of those on the legs, wings, 
and a few of those on the bases of the halteres. This type also 
includes all of those found in the other three orders examined. 
The other three types are found on the bases of the halteres. 
The undetermined type really belongs to the Hicks’ type, while 
the basal type is very similar to the Hicks’ type; nevertheless, 
the basal and scalpel types are quite unique and are found only 
on the halteres. While the basal pores stand in rows resembling 
the shape of mountain ranges, each row of the scalpel pores may 
be likened to an inverted urn-shaped ridge whose summit is 
more or less flat and is beautifully sculptured. Deep depressions 
lie between the rows in each type and a row of strong, protective 
pseudohairs stands in each depression. Morphologically, the 
scalpel type is the most highly developed, but physiologically 
it is probably little or no better developed than any other type of 
pore. 
This study indicates that while the hind wings of Diptera have 
been gradually reduced in size, consequently diminishing their 
flying ability, their sensory function has been greatly increased. 
Compared with the antennal organs, the olfactory pores are 
better adapted anatomically to receive olfactory stimuli, because 
the peripheral ends of their sense fibers come in direct contact 
with the external air, while those in the antennal organs are cov- 
ered with hard chitin. 
