STRUCTURE 97 



complex middle part of the lip by amalgamation with the para- 

 glossae. It has recently been proposed to treat this lingua as the 

 morphological equivalent of the labium or of the maxillae, giving 

 it the name of the endolabium, but the propriety of this course 

 remains to be proved ; ^ the view is apparently suggested chiefly 

 by the structure of the mouth of Hemimerus, a very rare and 

 most peculiar Insect that has not as yet been sufficiently studied. 

 As the maxillae and labium are largely used by taxonomists 

 in the systematic arrangement of the mandibulate Insects, we 

 give a figure of them as seen in Coleoptera, where the parts, 

 though closely amalgamated, can nevertheless be distinguished. 

 This Fig. 52 should be compared with Fig. 51. 



In speaking of the segments of the body we pointed out 

 that they were not separate parts but constituted an uninter- 

 rupted whole, and it is well to remark here that this is also 

 true of the gnathites. Although the mouth parts are spoken of 

 as separate pieces, they really form only projections from the 

 great body wall. Fig. 51, B, shows the intimate connexion 

 that exists between the maxillae and labium ; the continuity 

 of the mandibles with the membrane of the buccal cavity is 

 capable of very easy demonstration. 



The head bears, besides the pieces we have considered, a pair 

 of antennae. These organs, though varying excessively in form, 

 are always present in the adult Insect, and exist even in the 

 majority of young Insects. They are very mobile, highly sensitive 

 organs, situate on or near the front part of the head. The 

 antennae arise in the embryo from the procephalic lobes, the 

 morphological import of whicli parts is one of the most difficult 

 points connected with Insect embryology. 



The eyes of Insects are of two sorts, simple and compound. 

 The simple eyes, or ocelli, vary in number from one to as many 

 as eighteen or twenty ; when thus numerous they are situated in 

 groups on each side of the head. In their most perfect form, as 

 found in adult aculeate Hymenoptera, in Orthoptera and Diptera, 

 ocelli are usually two or three in number, and present the 

 appearance of small, perfectly transparent lenses inserted in the 

 integument. In their simplest form they are said to consist of 

 some masses of pigment in connexion with a nerve. 



The compound, or facetted, eyes are the most remarkable of all 



^ See on this subject, p. 217. 

 VOL. V ^ 



