Development and Metamorphosis 



47 



in its closed cell for thirteen days, and then it awakens to active life, gnaws 

 its way through the cell-cap and issues into the hive-space a definitive honey- 

 bee with all the wonderful special structures that make the honey-bee body 

 such an effective little insectean machine. The blow-fly (Fig. 76) lays a hun- 

 dred or more little white eggs on exposed meat. From these eggs come in 

 twenty or thirty hours the tiny white wriggling larvae (maggots), footless, eye- 

 less, wingless, nearly headless, with a single pair of curious extensile hooks 

 for mouth-parts. For ten to fourteen days these larvae squirm and feed and 

 grow, moulting twice in this time; they then pupate inside of the larval 

 cuticle, which becomes thicker, firmer, and brown, so as to enclose the deli- 

 cate pupa in a stout protective shell. The blow-fly now looks like a small 

 thick spindle-shaped seed or bean, and this stage lasts for twelve or fourteen 



kmth 



hjiuv. 



\kmt.L 



.-..., ^Ih-miJt 

 kml.l. lun.L 



B C 



FIG. 79. Dipterous larvae showing (through skin) the imaginal discs or buds of wings, 

 these buds being just inside the skin. A, larva of black fly, Simulium sp.; B, anterior 

 end of larva of midge, Chironomus sp.; C, anterior end, cut open, of larva of giant 

 crane-fly, Holorusia rubiginosa; h.pr., bud of prothoracic respiratory tube; h .pi., 

 bud of prothoracic leg; h.m-w., bud of mesothoracic wing; h.ml., bud of mesothoracic 

 leg; h.mtb., bud of metathoracic balancer; h.mtl., bud of metathoracic leg. (Much 

 enlarged.) 



days. Then the winged imago, the buzzing blow-fly, as we best know it, 

 breaks its way out. In the house-fly the same kind of life-history, with 

 complete metamorphosis of the extremest type, is completed in ten days. 

 Nor do we realize how really extreme and extraordinary this metamorpho- 

 sis is until we study the changes which take place inside the body, as well 

 as those superficial ones we have already noted. 



The natural question occurs to the thoughtful reader: "Is the meta- 

 morphosis or transformation in the postembryonal development of such 

 insects as the butterfly, bee, and blow-fly as sudden or discontinuous and 

 as radical as the superficial phenomena indicate? " The answer is no, and 

 yes; the metamorphosis is not so discontinuous or saltatory and yet is 

 even more radical and fundamental than the external changes suggest. To 



