674 EXTERNAL ANATOMY OF INSECTS. 
Dytiscus serricornis internally; in Necydalis barpipes 
this fringe is longer at the apex; and in Saperda hirti- 
pes the same ¢ibie at that part are adorned with a large 
brush, like that observable in the antennee of some 
Lamie*. 
I must next call your attention to the teeth, spines, 
and spurs with which the ézbie of insects are sometimes 
armed. With regard to ¢eeth, you have doubtless often 
observed those that distinguish the cubitus of the arm of 
most Lamellicorn beetles: these vary in number from 
one, as in Trox suberosus, to seven as in Geotrupes, autum- 
nalis ; but the most universal number is three: im some 
species of the genus last named, as G. stercorarius, &c., 
the ¢hird tooth from the apex, and those that follow it, 
may be called double. These teeth, in their cubit or an- 
terior shank, doubtless assist these insects in burrowing. 
The four posterior ¢#bie in this tribe are also distin- 
guished by a kind of teeth which occupy their whole 
diameter, and resemble so many steps. I have before 
noticed the remarkable cubit of the Gryllotalpa, and 
likewise that of Scarites, Pasimachus, &c., in which some 
of the teeth are prolonged into spznes®, which are the next 
description of tibial arms that I mentioned. Spines are 
of two kinds—those which are merely processes of the 
crust of the ¢7bza, and those that are zmplanted in it, and 
seem to have a gomphosis or perhaps an amphiarthrosis 
articulation ®. An instance of the frst kind may be seen 
in the hind-legs of some grasshoppers ¢ (Locusta), the 
® Oliv. Jus. n. 68, ¢. i. f. 8. comp. n. 67. ¢. xii. f. 83. and Pirate 
XII. Fic. 25. a. > Vor. II. p. 361—. and Prate XV. Fie, 5. 6. 
* See above, p. 432, Note b. and 403, Note a. 
@ Pirate XIV. Fie, 5, 
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