1 6 AN INTRODUCTION TO ENTOMOLOGY. 



Sometimes, however, the paraglossae are large, exceeding the glossa in size 

 From the base of the ligula arise a pair of appendages, the labial palpi (d). 

 Each labial palpus consists of from one to four freely movable segments. 



In the form of the labium just described, the correspondence of its parts to 

 the parts of the maxillae is not easily seen ; but this is much more evident in 

 the labium of some of the lower insects, as for example a cockroach (Fig. 30). 

 Here the organ is very deeply cleft ; only the submentum 

 and mentum remain united on the median line ; while the 

 ligula consists of two distinct maxilla-like parts. It is 

 easy in this case to trace the correspondence referred 

 to above. Each lateral half of the submentum corre- 

 sponds to the cardo of a maxilla ; each half of the mentum, 

 to the stipes ; while the remaining parts of a maxilla are 

 represented by each half of the ligula, as follows : near 

 the base of the ligula there is a part (c 1 ) which bears the 

 Fig. 3o.—Labium of labial palpus ; this appears in the figure like a basal segment 

 of the palpus ; but in many insects it is easily seen that it 

 is undoubtedly one of the primary parts of the organ ; it has been named the 

 palpiger, and is the homologue of the palpifer of a maxilla. The trunk of each 

 half of the ligula is formed by a large sclerite (c k ) to which I believe attention 

 has not been called heretofore. This evidently corresponds to the subgalea. 

 At the distal extremity of this subgalea of the labium there are two append- 

 ages. The lateral one of these (c s ) is the paraglossa, and obviously corre- 

 sponds to the galea. The mesal one (c 2 ) corresponds to the lacinia or inner 

 lobe. This part is probably wanting in those insects in which the glossa con- 

 sists of an undivided part; and in this case the glossa probably represents the 

 united and more or less elongated subgaleae. 



The Epipharynx and the Hypopharynx. — In addition to the mouth-parts 

 described above, either the labrum or the labium may bear on its ental surface, 

 within the cavity of the mouth, a more or less tongue-like organ. If borne by 

 the labrum, it is termed the epipharynx (9) ; if by the labium, the hypopharynx 

 (13). (See Fig. 22.) The epipharynx and the hypopharynx are rarely both 

 developed in the same insect, except in some Hymenoptera. The form and 

 position of the hypopharynx are analogous to those of the tongue of higher 

 animals. On this account it has been named the lingua or tongue. But as 

 both of these terms have been applied to the glossa, it is best to designate this 

 part as the hypopharynx, and to avoid the use of the terms lingua and tongue, 

 as liable to be ambiguous. 



The Thorax. 



The thorax is the second or intermediate region of the body. It 

 is readily distinguished by its appendages, which are three pairs of 

 legs and one or two pairs of wings. This region consists of three 

 segments. The cephalic or first segment is named the protJwrax 

 (14) ; the second, the mcsothorax (15) ; and the third, the mctatJwrax 

 (16). Each segment bears a pair of legs ; and in winged insects the 

 wings are borne by the second and third segments. 



