742 EXTERNAL ANATOMY OF INSECTS. 
lobes*. In Edessa, another genus of bugs, the ab- 
domen usually terminates in four strong sharp denti- 
form spines, the intermediate ones being the shortest, 
and in some the margin is also armed with spines ?; 
occasionally the anal spines are very long*. In addition 
to the ventral horns before mentioned that distinguish 
the sexes of some insects‘; the males of the genus Conops, 
a two-winged fly, have, on the antepenultimate ventral 
segment, a singular process, varying in length and shape 
in the different species, standing nearly at right angles 
with the belly, convex towards the trunk, and concave 
towards the anus. De Geer supposes that with the anal 
extremity this forms a forceps with which this fly seizes 
the other sex °. 
2. Organs of respiration’. I shall defer my account 
of the spzracles, and other external respiratory organs, 
till I come to treat of the system of respzration in insects, 
when every thing connected with that subject will be 
most properly discussed ; but there are certain appear- 
ances in some insects, which at first sight seem to par- 
take of the same character, but which being really inde- 
pendent of that vital function, may here have their place. 
If you examine the abdomen of the mole-cricket (Gryllo- 
talpa vulgaris), you will easily discover the true spiracles 
in the folds of the pulmonarium, which separates the back 
of that part from the belly; if you next inspect the five 
intermediate segments of the latter, you will discover 
‘on each nearer the base a pair of oblique little chan- 
nels, which precisely resemble closed spiracles. These 
* Stoll Punaises, t. xiii. f. 101. b Ibid. t. xvii. f. 117. 
© Tid. t. xxxvi. f. 253. 4 See above, p. 338 —. 
© De Geer, vi. 260. ¢. xv. f. 8. d. £ Prate XXIX. 
