EXTERNAL ANATOMY OF INSECTS. 513 
base?. In the water-scorpions (Nepa Belostoma, &c.) 
they may be called extraocular, being placed under the 
head in its prone part, outside the eyes”. In Nzrmus 
Fringille, a kind of bird-louse, they appear to be oral, 
being situated, according to De Geer, under the head 
near the mouth, at a great distance from the eyes °. 
In their proportions, both as to length and thickness, 
antennz: vary extremely. Thus sometimes they are very 
short—much shorter than the head; as in the aquatic 
beetles Gyrinus, Parnus, and the water-scorpion ; and 
some land-beetles, as Anthrenus, &c. At other times they 
far exceed the length of the insect: the males of many 
Capricorn beetles are so distinguished. In that of Acan- 
thocinus edilis they are more than four times as long as 
the body; and every intermediate length between these 
two may be found amongst them. They vary also greatly 
in thickness : in Paussus, whose antennze emit light in the 
night’, and Cerapterus, they are nearly as thick,—at 
least their knob, which forms the chief part of them,—as 
the body of the insect*; while in Mantis, Acrida, and 
Psocus, they are as slender as a hair. ‘The antennz in 
many of the Przonz, especially in P. imbricornis, are 
equally thick from base to tip; while in other Capricorn 
beetles they are quite the reverse. 
It will not be necessary to enlarge here upon the ge- 
neral form of these organs: I shall therefore only notice 
the two principal divisions of them in this respect.— 
Antennz, regard being had to one of their uses, may be 
* Oliv. Ins. no. 80. Macrocephalus t.i. f. 1—4; Anthribus f.5—12; 
and no. 83. Curculio t. ii. Calandra f. 16. 
> Schellenberg Cimices t. xiv. f. 1. 8. 
© De Geer vii. ¢. iv. f. 7. aa. 4 Vor. II. p. 416, 419. 
* Prares XII, Fic. 28; and XXV. Fic. 9, 24. 
WOU. 111. ee 
