INSECTA. 165 



different insects. They appear to be certainly organs of touch, but 

 they very probably minister to other senses as well, and there is 

 some reason to suppose that they are connected with the sense of 

 hearing in particular. 



The sexes in insects are distinct, and most of them are oviparous. 

 Generally speaking, the young insect is extremely different in ex- 

 ternal characters from the adult, and it requires, before reaching 

 maturity, to pass through a series of changes which collectively con- 

 stitute what is called the " metamorphosis." In some insects, how- 

 ever, there is no proper metamorphosis, and in some the changes 

 which take place are not so complete and striking as in others. By 

 the absence of metamorphosis, or by its completeness when present, 

 insects are divided into three convenient, though perhaps not strictly 

 natural, sections, as follows : — 



Section I. AmetahoKc Insects. — The insects belonging to this section 

 are said to be " Ametabolic " (Gr. a, without ; metabole, change), 

 because they pass through no metamorphosis. The young, on their 

 escape from the egg, resemble the adult in every respect, except in 

 size, and they undergo no alteration in reaching maturity, except 

 that they grow largei'. All the insects of this section are desti- 

 tute of wings in the adult state, and they are therefore often called 

 " Aptera " (Gr. a, without ; pteron, a wihg). 



Section II. Hemimetaholic Insects. — In the insects belonging to 

 this section (Gr. hemi, half ; and metahoU, change), there is a meta- 

 morphosis consisting of three stages, but these stages do not differ 

 much from one another in appearance (see fig. 117). The young, on 

 escaping from the egg, is known as the " larva," and it is not only 

 much smaller than the adult, but is destitute of wings. After 

 several changes of skin, the larva enters into the second stage, when 

 it is termed the " pupa.'' The pupa is active and locomotive, and 

 rarely differs much from the larva, except that it is bigger, and that 

 rudimentary wings have now appeared on the back of the thorax. 

 After a certain period, and after some changes of skin, the wings 

 burst from their sheaths, and the pupa is now converted into the 

 third and final stage, when it is known as the " imago " or perfect 

 insect. In all the insects belonging to this section — such as Grass- 

 hoppers, Dragon-flies, &c. — the second stage, or pupa, is active and 

 locomotive ; and for this reason the metamorphosis is said to be 

 " incomplete." 



Section III. HolometaboKc Insects (Gr. holos, entire ; and metabole', 

 change). — The insects belonging to this section — such as Butterflies, 



