THE OLFACTORY ORGANS OF DIPTERA 469 
ing the wingless forms (nos. 13 and 48), the mosquitoes (nos. 3 
to 5) differ from all the other Diptera examined in that each 
halter bears only one scalpel group instead of two. While the 
legs and wings of these mosquitoes are long and slender, the 
halteres are short and stout; relative to the other species exam- 
ined, the reverse is generally true. The number of pores on the 
halteres of mosquitoes is considerably less than the average 
number on the halteres of flies, but they appear to be consid- 
erably larger. Tipulidae is the only family which bears more 
pores on the legs than on either the wings or halteres. As a 
rule, the smaller species bear fewer pores than the larger ones, 
but there are many exceptions; for example, Tritoxa flexa (no. 
16) is one of the largest specimens examined, yet its total number 
of pores is among the lowest recorded. Among the genera the 
total number of pores may vary slightly, as in the mosquitoes 
(nos. 3 to 5) and in Anthomyidae, or considerably, as in Myce- 
tophilidae and Empididae; but among the species the total num- 
ber usually varies only slightly, as in nos. 24 and 25, 30 and 31, 
34 and 35, but occasionally a larger variation may be found, as in 
nos. 21 to 23 and 39 to 43. 
The olfactory pores on five females and five males of Musca 
domestica were carefully counted to determine the individual 
and sexua! variations. For the females the number of pores 
on the legs vary from 165 to 175 with 186 as an average; on the 
wings, from 219 to 274 with 252 as an average; on the halteres, 
from 530 to 570 with 552 as an average. For the males the 
number of pores on the legs vary from 168 to 180 with 172 as an 
average; on the wings, from 232 to 257 with 248 as an average; 
on the halteres, from 564 to 625 with 606 as an average. Thus, 
as an average a female bears 972 pores and a male 1026 pores. 
The mouth parts and antennae of many specimens were ex- 
amined, but no olfactory pores were seen on them. Other 
parts of the integuments besides those discussed were also often 
examined, although no olfactory pores were found on them, 
except on the ovipositor already mentioned (p. 467) and occa- 
sionally two or three pores on the thorax near the base of the 
wing. These were not carefully recorded and do not appear in 
the tables. 
