THE ORAL ORGANS OF THE GAD-FLY. 129 
ing to the lower, as the labrum does to the upper lip of a mandi- 
bulate insect. 
In general character and structure this organ resembles the well- 
known proboscis of the Blow-fly, and the comparison will perhaps 
serve better than an elaborate description. It is, however, relatively 
longer in the stalk, is not bent, but straight, and the terminal 
divided knob is somewhat differently placed. For some distance 
from the base it is supported by a chitinous structure analogous to 
the mentum, or chin, which has on each side a membranous flap 
continued and meeting further on, and at length forming the ex- 
ceedingly delicate membrane upon which the radiating system of 
suctorial semi-tubes is arranged. The outer surface of the membrane 
is thickly covered throughout, with the exception of the region of 
the tubes, with peculiar very short hairs arranged in groups, zor 
singly, as is usual. ‘That is to say, each minute hair, in place of 
being separately imbedded in the membrane, is grouped with 
several others on a common base which seems to project slightly 
itself above the surface. Near the tip again, are placed a number 
of strong bristles with well defined basal sockets. 
The labium, in fact, partly encloses the other.organs when at rest, 
they lying along its inner surface and between the terminal lips of 
the knob. According to Burmeister, the terminal lips are in reality 
differentiated labial palpi. 
We have here an apparatus well adapted in all its parts to the 
purpose ; first of all, of reaching the seat of the fluid nutriment 
necessary to the insect, and then of gathering it up and conveying 
it to the digestive tract. It should be stated, however, that only 
the female Gad-fly possesses the full complement of organs described. 
The male is destitute of mandibles, and I think I am right in saying, 
of maxillz also. Far from exhibiting the blood-thirsty instincts of 
the female, he is of a quiet, retiring disposition, preferring the 
shade of woods, and for food the juices of flowers. 
As to the special function of the different organs, I am unable 
to say much. Their strength, form, and size enable them to pene- 
trate the skin of most, if not all, British animals with comparative 
ease. ‘The mandibles are probably first brought into play to make 
an opening into which the barbed maxillz can then be plunged to 
enlarge and tear open the wound. The labrum and lingua seem to 
enter with the rest, and either by the lingua alone, or by the com- 
bined organs used as a tube, the blood is imbibed. The wound 
caused in this operation is sufficiently severe, but the formidable 
armature of the sete fully accounts for the pain and subsequent 
irritation which accompany the bite. 
A question here arises as to the function of the labium, if the 
lingua, or the other organs combined, must be regarded as suctorial. 
That it is itself capable of fulfilling a similar purpose cannot be 
