THE EXTERNAL ANATOMY OF INSECTS 



43 



The lahrum. — The Idbrum 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 Scarabceidae, each 

 mandible consists of several more or less distinct sclerites. 



The pardgnatha. — In some insects there is between the mandibles 

 and the maxillae a pair of more or less appendage-like organs borne by 

 the hypopharynx. These are 

 the "paraglossas" of writers on 

 the Thysanura and Collembola 

 and the "superhnguae" of Fol- 

 som ('00). They were termed 

 the maxillulae, a diminutive of 

 maxillas by Hansen ('93), who 

 regards them as homologous 

 with the first maxillae of the 

 Crustacea. But it has been 

 shown by Cramp ton ('21) that 

 they are homologous with the paragnatha of Crustacea. In 

 Figure 54, A. represents a ventral view of the hypopharynx, parag- 

 natha, and mandibles of the crustacean Ligyda; and B. the same 

 parts of a naiad of a May-fly, Heptagenia. Paragnatha have been 

 found in the Thysanura, Dermoptera, Orthoptera, Corrodentia, the 

 naiads of Ephemerida, and the lar\^£e of Coleoptera. 



The MaxillcB. — The maxUlcB are the second pair of jaws of insects. 

 Like the mandibles they are the appendages of one of the segments 

 of the head. 



Fig. 54. — A. Posterior (ventral) view of 

 mandibles and hypopharynx of the 

 crustacean Ligyda; h, hypopharynx; 

 p, paragnatha; m, mandibles; B. 

 Same of a nymph of the Mayfly 

 Heptagenia (From Crampton). 



The maxilte 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 hin^e, the stipes for foot- 

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

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



