EXTERNAL ANATOMY OF INSECTS. 713 



denticulated teeth ; and in Acanthia paradoxa by long 

 spinose lobes \ In Edessa F., another genus of bugs, 

 the abdomen usually terminates in four strong sharp 

 dentiform spines, the intermediate ones being the short- 

 est, and in some the margin is also armed with spines b ; 

 occasionally the anal spines are very long c . In addition 

 to the ventral horns before mentioned that distinguish 

 the sexes of some insects d ; 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 e . 



2. Organs of respiration f , I shall defer my account 

 of the spiracles, and other external respiratory organs, 

 till I come to treat of the system of respiration 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 heFe 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- 



a Stoll Punaises, t. xiii. / 101. b Ibid. t. xvii./. 117- 



c Ibid. t. xxxvi./. 253. d See above, p. 339—. 



e De Geer, vi. 260. t. xv./. 8. d. f Plate XXlX. 



