ON INDIAN PARASITIC I LIES. 
963 
is a bird parasite. They were separated from the Hippoboscidce by 
Kolenati (1862) and seem to form a natural group between that family 
and the Nycteribiidce which are more highly specialised and ex- 
clusively bat-parasites. They are, however, nearer the Hippobos- 
cids and are probably descended likewise from Muscid ancestors 
but along another line of descent. Some are destitute of eyes ; and 
where eyes are present the Streblids may usually be distinguished 
from the Hippoboscids by two fairly salient features. First, no 
Streblids have facetted compound eyes. Where the eyes are more 
than single ocelli they are formed by the agglomeration of several 
occelli. Secondly, in the Streblids the palpi do not sheathe the pro- 
boscis as they do in the Hippoboscids. 
A Streblid fly can often be recognised at a glance by the flattened 
leaflike pair of maxillary palpi which project in front of the head. 
Kolenati was certainly wrong when he suggested that the larval Streb- 
lids fed on the excrement of the bats ; they are pupiparous and their 
methods of reproduction are similar to those of the other families in 
that group. In some forms the legs are short and thick recalling 
those of the Hippoboscids ; in others they are enormously long and 
attenuated, or spider-like, recalling those of the Nycteribiids. It is 
of interest to note, in this connection, the two contrary lines along 
which the legs of ectoparasitic Diptera have evolved from the normal 
type in flies, the object in both cases, of course, being to secure a 
hold on the host. Wings in Streblids are sometimes well developed, 
sometimes reduced and sometimes absent. They are never much 
used as organs of locomotion ; and, where wings are well developed, 
they are covered with fine hairs which give a milky appearance rather 
rmusual among flies. Where the wings are reduced, the wing vena- 
tion is unlike that of the Hippoboscid wing, showing that reduction 
in this family has proceeded on other lines. Halteres are present 
but in the wingless species they are reduced. In many species of 
Streblid the halteres are protected by a projection of the thorax which 
may be regarded as an adaptation developed in connection with 
parasitic life to shield these delicate organs when the fly makes its 
way about the body of the host. The claws are always well developed ; 
and in one species, which is quite wingless, there is an indication of 
an accessory tooth. This is another illustration of the tendency 
among parasites to develop organs of prehension when organs of loco- 
motion are lost. 
The abdomen in this family shows little sign of segmentation except 
at the base where it is united to the thorax. In the winged species, 
the wings are contrived to fold back fan-wise and lie flat upon the 
surface of the insect’s back. With this, the arrangement of bristles 
on the dorsal surface of the abdomen seems to coincide ; for there 
is a bare tract along the back where the wings are tucked away. On 
