Chap. L] 
NYCTERIBIA. 
21 
known insect, and as its joints are so flexible as to yield 
in every direction (like what mechanics call a " ball and 
socket "), its motions are ex- 
ceedingly grotesque as it tum- 
bles through the fur of the 
bat. 
To enable it to attain its 
marvellous velocity, each foot 
is armed with two sharp hooks, 
with elastic opposable pads, so 
that the hair can not only be 
rapidly seized and firmly held, 
but as quickly disengaged, as 
the creature whirls away in its headlong career. 
The insects to which it bears the nearest affinity, are 
the Hippobosciclce, or " spider flies," that infest birds and 
horses ; but, unlike them, the Nycteribia is unable to fly. 
Its strangest peculiarity, and that which gave rise to 
the belief that it was headless, is its faculty when at rest 
of throwing back its head and pressing it close between 
its shoulders till the under side becomes uppermost, not 
a vestige of head being discernible where we would 
naturally look for it, and the whole seeming but a 
casual inequality on its back. 
On closer examination this apparent tubercle is 
found to have a leathery attachment like a flexible neck, 
and by a sudden jerk the little creature is enabled to 
project it forward into its normal position, when it is 
discovered to be furnished with a mouth, antennse, and 
four eyes, two on each side. 
The organisation of such an insect is a marvellous 
adaptation of physical form to special circumstances. 
As the nycteribia has to make its way through fur and 
c 3 
