EXTERNAL ANATOMY OF INSECTS. 507 
In those male flies (Mascida) 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? : in others, again, 
it is obtusangular, as you will see in Pepsis and various 
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 ¢wo, 
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 that have them.—They are often 
distant, as in Scutellera and Edessa ; and sometimes ap- 
proximaied, as in Reduvius®. In many of the homopter- 
ous Hemiptera, as Cercopis, Ledra, &c. they are planted 
in the wpper part of the head‘, but in Zassus their situa- 
tion is on the wnder part; and in a North American 
subgenus, as yet without a name, they are exactly de- 
tween the two, being placed in the frontal angle. In 
Fulgora their station is between the eyes and antenne‘. 
They are most commonly sessile, and as it were set in 
the head ; but in some, as Fulgora candelaria, they stand 
on a footstalk. 'The stemmata are set in the side of a 
frontal tubercle in that four-winged fly of threatening 
aspect, Corydalis, which in its perfect state has mandi- 
bles, but longer and more tremendous, like those that 
* Prare VI. Fic. 4. 1. - >’ Prave XXVF. Fic. 40, 1. 
© Ibid, Fic. 42. i. 4 Tbid. Fie. 41.1. ad 
