INSECTS IN GENERAL 13 



called a caterpillar. When it is almost or completely 

 legless, soft as to the cuticle, but with a hard head 

 and well developed mouth -parts, the word grub may 

 be employed. And when all trace of limbs of any 

 kind have disappeared, while the head and its appen- 

 dages evince signs of much simplification, the larva is 

 usually spoken of as a maggot. In like manner the 

 pupa of a butterfly is often called a chrysalis ; strictly 

 speaking, however, this term can only be used to 

 describe pupae (like those of the " tortoiseshells " and 

 " fritillaries ") that have brilliant metal-like areas on 

 their surfaces, since it is derived from a Greek word 

 signifying "gold." 



The facts of growth and development which have 

 been briefly set forth above appear to indicate that 

 metamorphosis was not a feature of the primitive 

 insect's life-history. The lowliest existing insects 

 have no metamorphosis ; higher in the scale meta- 

 morphosis is slight, or incomplete, while only among 

 the more highly specialized forms is it strongly 

 marked, or complete. From this we are led to infer 

 that metamorphosis is not a necessary concomitant of 

 growth and development, but a " special adaptation " 

 to peculiar and transitory needs. The habits and 

 surroundings of the young cockroach or mole-cricket 

 are practically identical with those of its parents. 

 Thus, it need not differ from them in form or faculty. 

 But among the higher insects the environment and 

 food-habits of the young constitute a unique phase in 

 the life-history. The dragon-fly nymph dwells in the 

 water, gaining its livelihood rather by stealth than by 

 alertness, whereas the adult dragon-fly spends most 

 of its time hawking insects in the air ; the caterpillar 

 chews up leaves, while the butterfly sucks nectar 



