36o CHARACTERS OF INVERTEBRATE ANIMALS 



an extremely short pair of antennae, a group of simple eyes on 

 each side, and biting mouth -parts. The cylindrical trunk is 

 composed of eleven segments, the first three of which bear 

 jointed legs corresponding to those of the adult; and besides 

 this, from one to five of the other segments possess stumpy pro- 

 legs which have sucker-like ends. Those at the posterior end 

 of the body are often modified in various ways. 



Caterpillars vary much in size, colour, and other characters, 

 among which may be mentioned presence or absence of hairs, 

 some being smooth and hairless, and others so hirsute as to 

 have earned the popular name of " woolly bears ". After leading 

 a life entirely devoted to continuous feeding for a period varying 

 from weeks to years, during which time the skin is frequently 

 moulted as the body increases in size, the caterpillar becomes 

 lethargic and passes into the quiescent pupa stage, constituting 

 what is generally called a chrysalis. A continuous horny covering 

 invests body and limbs alike, beneath which the parts of the 

 perfect insect can be dimly traced. Innumerable methods of 

 concealment and protection ward off to some extent the attacks 

 of enemies during this helpless period. In some cases the 

 chrysalis is to be found above-ground suspended by a silken cord, 

 or fastened to some object by a girdle of the same material, in 

 which cases its colour commonly harmonizes with the surround- 

 ings and renders it inconspicuous. Other chrysalides are sheltered 

 underground, and others again are to be found within cocoons, of 

 which the silkworm is the most familiar illustration. 



The last stage is reached when the perfect insect or imago 

 issues from the chrysalis at a time dependent upon favourable 

 conditions of temperature and various other factors, such, e.g., 

 as a suitable state of the particular food-plant upon which the 

 eggs are laid. 



The most convenient way of subdividing Lepidoptera is into 

 the two groups of (i) Butterflies (Rhopalocera) and (2) Moths 

 (Heterocera), of which the latter include a very much greater 

 number of species, there being in Britain, for example, over 

 1900 sorts of Moths as against between sixty and seventy species 

 of Butterflies. 



I. Butterflies (Rhopalocera). — Butterflies for the most part 

 are active in the daytime, especially during sunny weather. 

 They can readily be distinguished from Moths by the antennae, 



