410 Animal Biology 



species^ one or two organs, the membranous epipharynx and the tongue- 

 like hypopharynx (Fig. 202). The jaws operate horizontally rather than 

 up and down. The maxillae and labium are each supplied with a pair 

 of sensitive feelers {palpi). Mouth parts vary greatly with the different 

 species. Among certain insects with sucking mouth parts, there are varia- 

 tions. For example, in the mosquito (order Diptera) (Fig. 202) the 

 mouth parts are modified for piercing in addition to sucking, while the 

 butterfly (order Hymenoptera) (Fig. 201) sucks nectar from flowers with 

 a tubular proboscis. 



Antennae 

 A 



_ CorDpound eye 



:^ Labial palpus 



_ Proboscis 



Fig. 201. — Butterfly head and mouth parts, the latter in the form of a siphoning 

 (sucking) proboscis which may be uncoiled when used. 



Many insects in their life cycles undergo remarkable changes in form 

 and size. These changes in structure and form undergone by an organism 

 from the embryo to the adult stage constitute metamorphosis (met a- 

 mor'fosis) (Gr. meta, change; morphe^, form). The life cycle (Gr. 

 kyklos, circle) includes the various stages through which an individual 

 passes from one adult stage to the next aduU stage. There are diff"erent 

 systems of classifying the types of insect metamorphosis but the following 

 is typical: 



i. No Metamorphosis. — In this type the egg develops into a form 

 which is practically the same as the adult, although smaller. Briefly, the 

 stages are egg, adult, egg (Figs. 203, 204, 273, 274) . 



