64 CATERPILLARS AND THEIR MOTHS 



worms. That is, ages ago some of these worms varied 

 from the regular type, for one of the natural laws is 

 that there is a tendency to vary among individuals of 

 the same species and even of the same brood. As the 

 conditions of the earth's surface and climate changed, 

 those worms which had varied in ways which made 

 them fittest to bear these changes survived, while the 

 least fit died. No one can tell how many species have 

 become extinct in this way. 



The changed conditions caused variations in the 

 creatures, as well as made them necessary, and as 

 changes were constantly occurring, though they were 

 slow, new species were developed from the old forms un- 

 til they reached the stages in which we see them to-day, 

 stages of much higher development than the worms 

 possess, with more complicated structure and far higher 

 powers. Therefore, though a caterpillar is a crawling 

 creature, and though some dictionaries allow all crawl- 

 ing creatures to be called worms, it is not fair or just 

 to call them so. Names like " canker-worm," " fall 

 web-worm," and " silk- worm " have become a part of 

 our language, and will be used by all sorts of writers 

 and in talking, but we need not perpetuate the mis- 

 take and the injustice of calling all caterpillars 

 " worms." 



The changes from caterpillar to pupa and from 

 pupa to moth are called metamorphoses, and are 

 thought to have been caused originally by changes of 

 food, of surroundings, and of hot and cold seasons, as 

 well as by other changing conditions. 



In order to continue the life of the species, moths 

 must survive the winter in some form not requiring 



