GENERAL EXTERNAL STRUCTURE OF INSECTS. 



17 



The maxillae (fig. 3 B and B) are complicated appendages in their 

 typical form. Each consists of a principal piece called the stipes {St) , 

 which is hinged to the head by means of a smaller basal piece, the 

 cardo {Cd). Terminally the stipes bears an outer lobe, the galea 

 {Ga), and an inner lobe, the lacin'm (Lc). On the outer side, at the 

 base of the galea, it carries a jointed appendage called the maxillary 

 palpus (Pip). 



The hypopharynx (fig. 3 C and D, Hphy) is a median, ventral, 

 tonguelike organ, called also the lingua, situated either on the upper 

 surface of the labium or on the membrane between this organ and the 

 mouth. It is de- 

 veloped principally 

 from a median lobe 

 of the head of the 

 embryo behind the 

 mouth (fig. 2, Lin), 

 but some entomol- 

 ogists claim that it 

 is compounded of 

 this lobe and two 

 smaller lateral ones 

 developed from the 

 appendages of the 

 fifth embryonic 

 head segment (fig. 

 2, Slin), the super- 

 Unguce. 



The labium (fig. 

 3 C and D) consti- 

 tutes the under lip 

 of the adult, but it 

 is formed from the 

 two appendages of 

 the seventh segment in the embryo, which fuse with each other. For 

 this reason it is often called the second maxillce. It consists of a basal 

 suhnventum (Snit) bearing the mentum (Mt), which in turn carries 

 three parts, a median ligula {Lg) and two lateral palpigers {Pig). 

 The latter support the labial palpi {Pip), while the ligula bears four 

 terminal lobes, of which the median ones are called the glossce {Gls) 

 and the lateral ones the paraglosscB {Pgl). If we should cut the 

 labium into two parts along its midline we should see that even in 

 the adult stage each half is very similar to one maxilla. The only 

 discrepancy to be noticed in the example given (fig. 3) is that there 

 22181— No. 18—10 2 



Pip 



Fig. 3. — Example of generalized insect mouth parts, from 

 common black cricket (Gryllus pennsylvanicus) : A, man- 

 dibles ; B, B, maxillae, ventral view ; C, labium or second 

 maxillffi, ventral view ; D, labium, lateral view. 



