THE EXTERNAL ANATOMY OF INSECTS 



43 



The labrum. The Idbritm or upper lip (Fig. 53), is a more or less 

 flap-like organ above the opening of the mouth. As it is often freely 

 movable, it has the appearance of an appendage of the body; but it 

 is not a true appendage, being a part of one of the body segments that 

 enter into the composition of the head. 



The mandibles. The mandibles are the upper pair of jaws (Fig. 

 53). They represent the appendages of one of the segments of the 

 head. In most cases they are reduced to a single segment; but in 

 some insects, as in certain beetles of the family Scarabaeidae, each 

 mandible consists of several more or less distinct sclerites. 



lu The maxillula. The maxilhila are a pair of appendages, which 

 when present are situated between the mandibles and the maxillae. 

 With most insects they are either absent or are so slightly developed 

 that they do not have the appearance of appendages, and have been 

 considered as merely lateral lobes of the hypopharnyx. Borner ('04) 

 finds that the hypopharynx of nearly all insects having an incomplete 

 metamorphosis bears a pair of vestigial maxillulae; maxillulae have 

 been found in the Thysanura, Dermaptera, Orthoptera, Corrodentia, 

 the naiads of Ephemerida, and the larvae of 

 Coleoptera. 



In certain Thysanura the maxillulae are 

 well -preserved; figure 54 represents a maxillula 

 of Machilis maritima. These appendages are 

 the "paraglossce" of writers on the Thysanura 

 and Collembola and the superlingutB of Folsom 

 Coo). 



The term maxillulae, a diminutive of maxillae, was 

 proposed by Hansen ('93), who regards them as homo- 

 logous with the first maxillae of the Crustaceae. They 

 are the appendages of a segment of the head which is 

 very slightly developed in most insects. 



The maxillae. The maxilla are the second 



pair of jaws of most insects, of all insects except Fi ?-, 54- ;5ifiJ*. maxil- 

 - , . , .,, . _ ., lula of Mac mlis man- 



those in which the maxillulae are retained. Like 



~ga 



la- 



the mandibles they are the appendages of one 

 of the segments of the head. 



tima; la, lacinia; ga, 

 galea; p, palpus 

 (After Carpenter) . 



The maxillae are much more complicated than the mandibles, each maxilla 

 consisting, when all of the parts are present, of five primary parts and three 

 appendages. The primary parts are the cardo or hinge, the stipes or foot- 

 stalk, the palpifer or palpus-bearer, the subgalea or helmet-bearer, and the 

 lacinia or blade. The appendages are the maxillary palpus or feeler, the galea 



