INTKODUCTION. XXIX 



The head is very variable in form, especially in the Homoptera, 

 and particularly iu the rulgoridae, in which family it is inflated and 

 produced in a way for Avhich at present no absolute explanation 

 can be offered. In the Heteroptera the head is usually more or 

 less triangular in shape, but exceptions occur in all the families. It 

 varies in prolongation and constriction, and although the eyes are 

 generally placed at or near the anterior margin of the pronotum, 

 there are genera in which they are far remote from the pronotal 

 margin. It also varies in its direction as well as shape : in 

 some species it is horizontally produced, in others obliquely 

 deflected, or again perpendicularly deflected ; and these three 

 forms of structure can be found in the Pentatomidae alone, without 

 I'eferring to other families. The head above is anteriorly composed 

 of three lobes — one central and two lateral ; or, as they are fre- 

 quently styled, respectively, the tylus and juga. Ocelli are usually 



Fig. 3. — Head, seen from above, of Catacanthus incarnahis. 



a. Central lobe {tyliis). a'. Lateral lobe {jugum). b. Eye. h'. Ocellus. 

 1, 2, 3, 4, 5. Antennal joints. 



present, but are sometimes wanting in a whole family, as in the 

 Pyrrhocoridse, or even absent in one genus of a small subfamily of 

 Pentatomidae, as for example in the Urostylinse. The compound 

 eyes vary much in position and shape. Grenacher has divided 

 the ej^es of insects into three divisions, according to the presence 

 or absence of a well-developed cone. Acone eyes are those in which 

 the cone or refracting body is wanting, but is represented by four 

 primitive cone-cells ; and according to Packard these occur in the 

 Ehynchota, exckuling the Homopterous Cicadidee, which have 

 Eucone eyes, distinguished by possessing a well-developed cone. 

 The antennae are usually free and visible, as in the Heteropterous 

 series Gymnocerata, or hidden in foveas under the head, as in 

 Cryptocerata ; sometimes, as in many Homoptera, they are minute 

 and hair-like. The antenniferous tubercles from which the antenna? 



