GROWTH AND TRANSFORMATIONS OF INSECTS 47 



growth of the grasshopper, on the other hand, is gradual and 

 presents no striking changes, and is known as an incomplete 

 metamorphosis. 



Growth. The hard, chitinous skin which serves the insect as 

 an outer skeleton has already been described, and furnishes an obvi- 

 ous obstacle to its rapid growth. When the insect has grown to 



the limit of this outer 

 shell, its predicament 

 is solved in the only 

 possible way, by the 

 skin splitting down the 

 middle of the back 

 and being sloughed 

 off, while the new skin 

 formed beneath the 

 old one allows further 



FIG. 57. Nymph of lubber grasshopper (Dictyophora p- rnwf u ^his nroress 



reticulata] ; similar to the adult (Fig. 103) in general & 1U ^ 



form, except in lacking wings Called molting, OCCUrs 



in all insects, as well 



as among other Arthropods, the skin being usually shed some 

 four or five times during growth, though some species molt from 

 ten to twenty times. 



Incomplete metamorphosis. Young insects which resemble the 

 adults, as those of the grasshopper, are termed nymphs. After the sec- 

 ond or third molt, small wing 

 pads appear on the back, 

 becoming much larger with 

 the fourth molt, and upon 



the fifth molt the adult FlG - 5 8 - A typical larva, the cotton bollworm 



or corn-ear worm; totally unlike the adult 



winged insect emerges, to moth in / orm 



feed and reproduce. 



Complete metamorphosis. The caterpillar, maggot, or grub bear- 

 ing no resemblance to its parents is called a larva. The larva 

 grows and molts several times, and although its new clothes are 

 sometimes of a different color, they are all cut on the same pattern, 

 and there is usually no marked change in shape or structure until 

 the larva is full grown. Upon reaching its growth the larva molts for 

 the last time and transforms into a pupa. The pupa is a dormant 



