Introduction to Animal Morphology. 397 



sharp differentiation of the thorax, assume its adult 

 form. Insects which only undergo changes like these 

 are called amdaboloiis. Other insects, while under- 

 going the growth of wings, c., lose embryonic 

 organs, and are called hemimetabolic. Most, how- 

 ever, differ very much in their larval and perfect states, 

 and the former passes through a quiescent or pupa 

 period before it becomes mature ; these are holome- 

 tabolic. The larvae, or caterpillars in general, are 

 annelid-like, nearly homonomous, with a soft skin, 

 and stumpy or no feet ; when present, the three an- 

 terior pair are often discriminable from the others 

 (which are called prolegs*),in shape and colour, and in 

 being several-jointed (often five). They are voracious, 

 with powerful jaws, a large stomach, and a large fatty 

 body ; they grow rapidly, and moult frequently. On 

 attaining their full size, those with labial silk-glands 

 spin a cocoon ; others become quiescent, inclosed in a 

 thickened skin, and cease to eat. This pupa or 

 chrysalis stage lasts until the internal organs attain 

 perfect development. They seem to undergo a nearly 

 perfect histolysis, and from certain areas of formative 

 6, called imaginal discs, rearrangement takes 

 place; then the pupa skin splits alone; the kirk, and 

 ,uago or perfect adult is produced. The pupa 

 may be//; t when the locomotory organs remain free 

 from th: trunk, as in 1 lymenoptero. and ( '<].< .? 

 or obtain! when these organs are inclosed in the 

 pupa, skin, and so are O In I.ej.id. 



coarctat, , \vh< ; up, v. ith 



no trace of li in 1 >ipt< ra. < to 



I'i : iir (Tenth: 



