THE EXTERNAL ANATOMY OF INSECTS 



43 



The labrum. The labrum 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. 



The majtittulcz. The maxtllula 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 ftave the appearance of appendages, and have been 

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

 finds that the hypopharvnx of nearly all insects having an incomplete 

 metamorphosis bears a ^air ofr' vestigial maxillulae; maxillulae have 

 been found in the Thysanura/ Dermaptera, Orthoptera, Corrodenti; 

 the naiads of EphemeridsAand the larvae of 

 Coleoptera. > 



In certain Thysanidra the\ maxillulae are 

 well-preserved; figure/54 represents a maxillula 

 of Machilis maritima. These appendages are 

 the " paraglossa" of writers on theVrhysanura 

 and Collembola ^d the superlingu<z\i Folsom 

 Coo). 



la- 



The term m^xillulas, a diminutive of maxmsi, was 

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

 logous withyftie first maxillae of the Crustaceae. \hey 

 are the ao|4ndages of a segment of the head which\is 

 very sligiuly developed in most insects. 



The maxilla. The maotilla are the second 



pair of jaws of most insects, of all insects except - 54- 



lula of Machilis man- 

 those in which the maxillulae are retained. Like tima; la, lacinia ; ga , 



the mandibles they are the appendages of one fjlea; ' p, palpus 

 / (After Carpenter), 



of the segments of the head. 



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 



