472 EXTERNAL ANATOMY OF INSECTS. 
the siphuncle, as fine as a hair, between them. This or- 
gan is of a type so dissimilar, as was before observed, to 
that of the Diptera in general, and approaches so near to 
that of the dog-tick (Jzedes), that they may be deemed ra- 
ther apterous insects with two wings, than to belong to that 
Order ; and the circumstance that some of the family are 
apterous confirms this idea. In fact they are a transition 
family that connects the two Orders, but are nearest to 
the Aptera. In Nyctertbia the oral organs differ from 
those of the other Pupipara in having palpi. This also 
is the case with those of the genus Jzodes, the palpi of 
which are placed upon the same base with the instru- 
ment of suction, than which they are longer: they ap- 
pear to consist of fwo joints, the last very long and flat. 
The instrument of suction itself is formed by three hard 
rigid laminee; two shorter parallel ones above, that co- 
ver the third, which is longer and broader, and armed 
on each side with several teeth like a saw, having their 
points towards the base*. Many of the other Acari L. 
have mandibles, and several have not: but their oral or- 
gans have not yet been sufficiently examined; and from 
the extreme minuteness of most of them, this is no easy 
task; nor to ascertain in what points they differ or 
agree. 
If you consider the general plan of the organs of man- 
ducation in the vertebrate animals, how few are the va- 
riations that it admits! An upper and a lower jaw 
planted with teeth, or a beak consisting of an upper or 
a lower mandible with a central tongue, form its princi- 
pal features. But in the little world of insects, how won- 
2 N. Dict. d’ Hist. Nat. xvi. 432. De Geer vii. f. vi. f. 4. Net 
guite accurate. 
