Mouth Organs of Insects. 53 



the pai-aglosssB (Fig. 35, d)^ one on eithei side. These 

 ai.e often wanting. 



The jaws or mandibles (Fig. 8,m,m) arise one on either 

 side just below and at the side of the labrum, or upper lip. 

 These work sidewise instead of up and down as in higher 

 animals, are frequently very hard and sharp, and sometimes 

 armed with one or more teeth. A rudimentary tooth 

 (Fig. 12, a, 6) is visible on the jaws of drone and queen 

 bees. 



Beneath the jaws or mandibles, and inserted a little far- 

 ther back, are the second jaws, or maxillae (Fig. 8, m,x), 

 less dense and firm than the mandibles, but far more com- 

 plex. Each maxilla arises bj' a small joint, the cardo; next 

 this is a larger joint, the stipes; from this extends on the 

 inside the broad lacinia (Fig. 35, c) or blade, usually fringed 

 with hairs on its inner edge, towards the mouth; while on 

 the outside of the stipes, is inserted the — from one to seve- 

 ral jointed — maxillary palpus. In the honey-bee the max- 

 illary palpi are very small and consist of two joints, and in 

 some insects are wholly wanting. Sometimes, as in some 

 of the beetles, there is a third piece running from the stipes 

 between the palpus and lacinia called the galea. The max- 

 illas also move sidewise, and probably aid in holding and 

 turning the food while it is crushed by the harder jaws, 

 though in some cases they, too, aid in triturating the food. 



These mouth-parts are very variable in form in different 

 insects. In butterflies and moths, two-winged flies and bugs, 

 they are transformed into a tube, which in the last two 

 groups forms a hard, strong beak or piercer, well exem- 

 plified in the mosquito and bed-bug. In all the other 

 insects we find them much as in the bees, with the sepa- 

 rate parts varying greatly in form, to agree with the habits 

 and character of their possessors. No wonder DeGeer 

 and Fabricius detected these varying forms as stronglj' 

 indicative of the nature of the insect, and no wonder that 

 by their use they were so successful in forming a natural 

 classification. 



If, as is more thac probable, the " Doctrine of Selection " 

 is well founded, then a change in habit is the precursor of 

 a change in structure. But what organs are so intimately 



