INSECTS. 249 



antennae. Their relative size is very different. Sometimes as in 

 Locustce, they exceed the length of the body, in others again they 

 are very short and almost concealed beneath the eyes. The form 

 likewise is different : the antennae are said to \>z filiform when they 

 are thin and of the same thickness throughout : clavate when they 

 have a knob at the end formed of thicker joints, as in butterflies 

 (Papiliones) , &c. 



The eyes (oculi) are either simple or compound. The simple 

 eyes are named eye-points (ocelli, stemmata) : they look like smooth 

 shining points placed usually in a triangle behind the larger eyes ; 

 they are seen in Bees, Wasps, &c. The larger eyes are composed 

 of numerous six-sided facettes, and are occasionally of such magni- 

 tude (as in Diptera, Libellulce), as to meet, the head seeming to 

 consist almost entirely of these two eyes. In some instances the 

 number of facettes is surprisingly great: LEEUWENHOECK counted 

 8000 in the eye of a fly, STRAUS nearly 8820 in that of a cockchafer 1 . 



The oral apparatus (organa cibaria, Trophi) consist of six 

 principal parts, of which four are in pairs and move transversely, 

 whilst two face each other above and below. Of these last the 

 uppermost is the upper lip (labrum) : it is horny and fixed by a 

 joint transversely to the most anterior part of the head. The part 

 of the head to which the upper lip is fastened is named head-shield 

 (clypeus, in French chaperon). The undermost part, facing the other, 

 is named the under lip (labiwn): it closes the mouth below: is 

 composed of two parts of which the inferior and more rigid is named 

 chin (mentum), and the superior,' generally membraneous, tongue 

 (ligida). Sometimes the ligula has two lateral lobes (paraglossce) . 

 The remaining four parts are known as upper and under jaws. The 

 upper jaws (mandibulce) are two, placed immediately beneath the 

 upper lip: they move transversely from within outwards, and are 

 often very hard. The under jaws (maxilla?) are ordinarily softer: 

 are placed beneath the mandibles, and also move laterally, but are 

 less serviceable for cutting the food small than for holding it in the 

 mouth and conveying it to the gullet to be swallowed. In the 

 Orthoptera there is a membraneous valve which is fastened to the 

 maxilla. It is called the helmet (galea) of the lower jaw. 



In addition to these principal parts there are also feelers (palpi, 



1 See plate xx. of SWAMMERDAM'S^/;^ der natuur, where the simple and com- 

 pound eyes of a bee are figured. 



