188 
hymenoptera. 
SEX 
The Mutillidw offer a striking example of that difference in 
structure connected with sex which is found in some form or another 
throughout the insect world. It is at first sight a striking thing to find 
that throughout a whole family, the female is wingless, but there are so 
many other striking differences that we may here draw the attention of 
the student to some salient points in this matter. 
We may omit here all reference to structures such as ovaries, clas- 
pers, ovipositors, etc., connected with the primary needs of mating and 
egg-laying ; these must obviously be present in every mature sexual 
form and on their examination must ultimately depend the determi¬ 
nation of sex. Apart from these structures, which are not always rea¬ 
dily discernible without dissection, there are a number of other differ¬ 
ences less immediately connected with the actual sexual functions and 
which are often more readily discernible. We may at once notice the 
wingless females, so marked a feature in Mutillidce. We are probably 
correct in saying that in this family the female has lost her wings since 
she does not require them in her search for the nests of her hosts but that 
the male retains them simply to aid him in his search for the female. 
The same is true of other forms, where the loss of wings appears to be 
an advantage but one which cannot be shared by the male as on him 
falls the work of seeking out his mate. Among Lepidoptera, the Psy- 
chidce are an excellent example and a few Lymantriidce exhibit the same 
phenomenon. All male Coccidce are winged, all females wingless ; many 
Pliasmidce have wingless females, while some of the species of the Re- 
duviid genus Physorhynchus are winged only in the male, though some 
other species of the genus are wingless in both sexes, the wings however 
more completely absent in the female than in the male, as if the former 
had lost them first. In the Lampyride division of Malacodermidce, 
wingless females are not uncommon and in some genera the females are 
practically unknown, only the males being found as winged beetles. 
Uzel mentions the exact reverse of this in Thysanoptera,where 
we find a wingless species in which some females become winged to dis¬ 
seminate the species. This reminds one of the Aphidce , where after a 
colony of wingless females is formed, winged females are found which 
fly away and start new colonies, though this last case is not connected 
with sex. 
The next notable point in sex is size ; here we have two groups, one 
in which the male is larger and the difference in size is connected with 
his functions ; the other in which the female is larger apparently because 
on her falls the more arduous task of providing for the offspring or 
because the mere bulk of eggs to be produced and carried necessitates 
a larger body. Large males at once suggest the Lucanidce (Stag beetles) 
and the Dynastidce, the great size being connected with the hypertro¬ 
phied mandibles or horns on the prothorax and head. Why these beetles 
