PROGRESSIVE MOTION IN INSECTS. 309 



which we meet with no example in other parts 

 of the animal kingdom. 



In attempting to delineate a sketch of the 

 movements of insects, and of the mechanism by 

 which they are performed, I am compelled, by 

 the great extent of the subject, to confine myself 

 to very general views ; and must refer such of 

 my readers as are desirous of fuller information 

 on this subject to the works of professed entomo- 

 logists. 



The mechanical conditions of an insect in its 

 several states of larva, pupa, and imago, are so 

 widely different, that it will be necessary to con- 

 sider each separately. In many tribes, however, 

 the difference between the larva and the perfect 

 insect is much less considerable than in others. 

 Those belonging to the orders of Hemiptera and 

 Orthoptera for example, come out of the egg 

 with nearly the same form as that which they 

 have in the mature state ; excepting that they 

 are without wings, these organs being added in 

 the progress of their growth, and constituting, 

 when acquired, their perfect or imago condition. 



§ 4. Aquatic Larvce. 



Many insects, which, when fully developed, are 

 the most perfectly constructed for flying, are, 

 when in the state of larvae, altogether aquatic 



