EXTERNAL ANATOMY OF INSECTS. 465 
follow the promusc?s till it gets beyond the forelegs, when 
it takes a direction perpendicular to the body?*; a cir- 
cumstance which has given rise to the above false notion. 
Though in Coccus, Chermes, &c. this instrument is short, 
in some Aphides it is longer in proportion than in any 
other insect. In A. Quercus it is three times the length 
of the body; so that when folded, it stretches out beyond 
it, and looks like a long tail”; and in A. Abzefzs it even 
exceeds that length °. 
~ ii, Proboscis4,—Linné long since, and after him Fa- 
bricius, has employed this term to designate the oral in- 
struments, or rather their sheath, in the Muscide and 
some others, calling the same organ, when without fleshy 
lips, rostrum and haustellum: but as the parts of the 
mouth in all true Diptera (for Hippobosca and its affinities 
can scarcely be deemed as co-ordinate with the rest,) are 
analogous to each other ; although in some they are stiff 
and rigid, in others flexile and soft, and in the Gstride 
(except the palpi) mere rudiments,—the same appella- 
tion ought to designate them all. I am happy to find 
that M. Latreille agrees with me in this opinion ; and to 
his sensible observations on this head, if you wish for 
further information, I refer you ®. The mouth of Di- 
pterous insects appears to vary in the number of pieces 
that it presents; but in all, the theca or sheath is present, 
which represents the Jabcum (including the mentum) of the 
“ De Geer iii. 137—. ¢. ix. f. 4. 
> Reaum. iii. 335. ¢. xxviii. f. 8—14. 
* De Geer iii. 117. ¢. viii. f. 22. 6. 
* Prare VII. Fie. 5, 6. a’, b’, ce’, d’. 
© N. Dict. d Hist. Nat. iv. 253. 
VOL. III. 2H 
