vi] LARVAE AND THEIR ADAPTATIONS 59 



minute booklets, arranged in a circular or crescentic 

 pattern, which assist the caterpillar in clinging to its 

 food-plant. The saw-fly caterpillar, on the other hand, 

 may have as many as eight pairs of pro-legs, the 

 series beginning on the second abdominal segment ; 

 here, however, the pro-legs have no booklets. Among 

 the Lepidoptera, we notice a reduction in the number 

 of pro-legs in the 'looper' caterpillars of Geometrid 

 moths. Here only two pairs are present, those on 

 the sixth and tenth abdominal segments. Conse- 

 quently, as the caterpillar can cling only by the 

 thorax and by the hinder region of the abdomen, the 

 middle region of the body is first straightened out 

 and then bent into an arch-like form, as the insect 

 makes its progress by alternate movements of stretch- 

 ing and 'looping.' 



Caterpillars, with their relatively soft bodies, 

 feeding openly on the leaves of plants, are exposed 

 to the attacks of many enemies, and the various 

 ways in which they obtain protection are well worth 

 studying. A clothing of hairs 1 or spines is often 

 present, and it is interesting to find that many 

 species of our native Tiger and Eggar Moths (Arctia- 

 dae and Lasiocampidae) which pass the winter in 

 the larval stage, have caterpillars with an especially 



1 The hairs ' of an insect are not in the least comparable to the 

 hairs of mammals, being in truth, modified portions of the cuticle, 

 secreted by special cells. 



