28 



NYMPHS. 



Fig. 19. NYMPHA. 



does not eat (jig. 19). Before under- 

 going this metamor'phosis, the larva 

 often prepares for itself a defence or 

 protection, and encloses itself in a shell 

 or cocoon (fg. 20), which it makes of 

 various materials ; but more especially 

 of the silk secreted by organs analo- 

 gous to salivary glands, and spun by 

 the assistance of spinnarets hollowed 

 in the lips. The insect, in the state 

 of a nympha, possesses all the parts 

 of the perfect animal, but contracted 



and covered up, sometimes by a delicate pellicle 

 through which they may be seen, giving the 

 nympha the appearance of a bandaged mummy; 

 sometimes by a pretty thick skin, which is 

 moulded over the body ; at other times, by the 

 dried skin of the larva, which forms a sort of 

 case or shell around the animal, presenting the 

 form of an egg. Finally, after having remained 

 in this state of immobility for a period varying 

 in duration, the "perfect insect (imago) escapes 

 from the nympha, and the external organs, at 

 first humid and soft, are dried by the air and 

 acquire the consistence they afterwards main- 

 tain. These changes in the external form of the insect at dif- 

 ferent periods of its life are accompanied by modifications, not 

 less remarkable, in the internal structure of the animal ; and 

 these changes of organization induce others in the habits of these 

 creatures as well as in the manner of feeding. 



57. The number of insects is immense ; it is estimated that it 

 exceeds sixty thousand species, and they differ very much from 

 each other both in their external form and manner of living. 



Insects, so remarkable for their organization, are still more so 

 for their habits and for the admirable instinct with which nature 

 has endowed a great number of them. Their cunning plans for 

 procuring food or for escaping their enemies, and the industry 

 they display in their works, surprise all who witness them; and 

 when we see them united in societies to gain the power denied to 

 their individual feebleness, aiding each other, dividing the toils 

 necessary for the prosperity of the community, providing for 

 their future wants, and frequently regulating their actions accord- 



Explanation of Fig. 20. A nympha with one-half of its shell or cocoon 

 emoved. 



Fig. 20. 



NYMPHA. 



57. What is the number of insects known ? 



