503 EXTERNAL ANATOMY OF INSECTS. 



pterous, as Tetyra, Pentatoma, Reduvius*, Cercopis, 

 Fulgora b , &c, have no more than two ; and in Larra 

 and its affinities, as just observed, the posterior ones are 

 obsolete, so as to leave only one discernible. 



Where there are three of these organs, they are usu- 

 ally arranged in an obverse triangle in the space behind 

 the antennae, at a greater or less distance from them. 

 In those male flies (Muscidce) whose eyes are confluent, 

 the stemmata are in a little area behind their conflux ; 

 but, as before observed, in the drone-bee and the Libel- 

 lulina they are before it. This triangle is in some cases 

 nearly equilateral, as in Perla related to the may-flies, 

 and many Hymenoptera ,• in others it is acutangular, as 

 in Locusta &c, in which the stemma forming the vertex 

 of the triangle is before the antenna c : in others, again, 

 it is obtusangular, as you will see in Pepsis and vari- 

 ous Hymenoptera. In the humble-bees (Bombus), a line 

 drawn through them would form a slight curve. Their 

 situation also varies. In insects that have only two, 

 they are sometimes placed a little behind the eyes, or in 

 the back part of the space between them : this is the case 

 with most of the bugs {Cimex L.) that have them. — 

 They are often distant, as in Tetyra F., Edessa F.; and 

 sometimes approximated, as in Reduvius F. d In many 

 of the Homopterous Hemiptera, as Cercopis, Ledra, &c. 

 they are planted in the upper part of the head e , but in 

 Iassus their situation is on the under part ; and in a North 

 American subgenus, as yet without a name, they are ex- 



« Plate XXVI. Fig. 40. i. 



b Cercopis, Ibid. Fig. 42; and Fulgora, Fig. 41. i. 



c Plate VI. Fig. 4. i. 



d Plate XXVI. Fig. 40. i. c Ibid. Fig. 42. i 



