20
are very much the same, although I have not been able to find some of the
smaller structures. The armature consists of two sets of petiolated blades
and one set of r od- l i ke sense hai r s. The pr oxi mal set of pet i ol at ed bl ades ar e
delicate leaf-like processes arising in pairs between the teeth, one pair
between each to adjacent teeth, and one pair external to the first
tooth. Their length is about the same as that of the teeth next
to which they lie, and they project distally so far that the tip
of the tooth is opposite the middle of the blade. Each blade arises from
the ridge of chitin to which the teeth are attached, at the point where the
bases of the teeth join with one another. The pairs arising between the sixth
and seventh and the seventh and eighth teeth are very much smaller than the
rest. The surface of the blades is finely granulated, but they do not appear
to have any coating of hairs. The distal set of blades are much larger and at
the same time much more delicate than the proximal ones, and arise from
longer stalks, so that their distal ends extend almost to the extreme limit of the
internal surface of the labellum. On account of their extreme delicacy it is
very difficult to make out their exact number and arrangement, for if one
examines them in uncleared preparations the opacity of the other structures
renders it impossible to trace them to their terminations, and in cleared pre
- p a r a t i o n s t h e y b e c o m e a l m o s t t r a n s p a r e n t . T h e r e a p p e a r t o b e s e v e n p a i r s , o f
which the second to the sixth are equal in size, the first rather smaller, and the
seventh less than half the size of the others. In shape they are similar to the
blades of the proximal set, their length being rather greater than that of the
teeth, their breadth about equal to that of the fifth and sixth teeth. The blade
ceases at a little distance beyond the apices of the teeth, and they are presum
- a b l y c o n n e c t e d w i t h t h e r i d g e o f c h i t i n a t t h e b a s e s o f t h e t e e t h b y a s t a l k ,
but this is either hidden from view by the blades of the first set or else is so
exceedingly delicate that it becomes invisible in cleared preparations.
The rod-like hairs resemble those of Stomoxysa n d
P h i l œ m a t o m y i a
, b u t
are relatively larger, being in fact the most conspicuous objects on the inner
surface, next to the teeth. Each arises from a short but broad cylindrical
base, and runs forwards and inwards so that it is raised a little from the
surface of the membrane, above the level of the teeth. One side of the hair
is deeply grooved, and the tip is bluntly rounded. I have not succeeded in
finding the nerve ganglion at the base of the hair, but doubtless it exists.
The membrane which forms the internal wall of the labellum, and on
which all these structures lie, is an extremely delicate and transparent one,
and is apparently structureless. It corresponds to the pseudo-tracheal mem
- b r a n e i n
M u s c a
, b u t s i n c e d i s t e n s i o n o f t h e l a b e l l a w i t h b l o o d n o l o n g e r
pays an important part in the mechanism of feeding, and since the size of the