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THE LIFE CYCLE 347 



13. Relative size of head, tliorax and abdomen, 

 expressed in the ratio, / -.x-.y. 



14. Antennse (relative development.) 



15. Mouthparts (adapted for biting or sucking, or 

 atrophied). 



16. Legs, (relative development). 



17. Lives where. 



18. Eats what. 



Write the forms in this table (by groups) in the order 

 of their departure from primitive similarity between larva 

 and adult. Fill out the table. Then study it, and read 

 out of it the story it contains of the divergence of larval 

 and adult stages, and in the last two columns under both 

 larva and adult, see how this divergence is correlated with 

 change of manner of life. 



The internal metamorphosis of insects. — While there is 

 no pupal stage in insects of incomplete metamorphosis, 

 such as the mayfly (fig. 200) , there is a corresponding period 

 just before transformation during which the full grown 

 nymph is quiescent for a short time, and during which there 

 is rapid growth of wing muscles and of other internal 

 organs; and some pupae, like those of the mosquitoes, caddis 

 flies and the true Neuroptera, are not wholly quiescent. 

 But in the pupas of all the more specialized forms, besides 

 the development of new tissues, there is going on a de- 

 struction of old ones that are not suited to the needs of the 

 adult and a reconstruction of their materials in new form. 

 The pupal stage thus becomes one of peculiar helplessness 

 in the life of the insect and it is spent in the shelter and 

 seclusion of a pupal cell or burrow or cocoon. Larval 

 life is abbreviated. The larva stores fat rapidly, and 

 in relatively large quantity, postponing the final elabora- 

 tion of it into organs. And the amount of fat in its body 



