118 HISTORY OF CRUSTACEA. Chap. XI. 



metamorpliosis still live upon the land or in fresh 

 water, as in the case of Gecarcinus, we may adopt the 

 latter. 



That besides this gradual extinction of the primitive 

 history, a falsification of the record preserved in the 

 developmental history takes place by means of the 

 struggle for existence which the free-living young 

 states have to undergo, requires no further exposition. 

 For it is perfectly evident that the struggle for exist- 

 ence and natural selection combined with this, must act 

 in the same way, in change and development, upon 

 Inrvae which have to provide for themselves, as upon 

 adult animals. The changes of the larvae, independent 

 of the progress of the adult animal, will become the 

 more considerable, the longer the duration of the life 

 of the larva in comparison to that of the adult animal, 

 the greater the difference in their mode of life, and the 

 more sharply marked the division of labour between 

 the different stages of development. These processes 

 have to a certain extent an action opposed to the 

 gradual extinction of the primitive history ; they in- 

 crease the differences between the individual stages of 

 development, and it will be easily seen how even a 

 straightforward course of development may be again 

 converted by them into a development with metamor- 

 phosis. By this means many, and it seems to me valid 

 reasons may be brought up in favour of the ojDinion 

 that the most ancient Insects ap]Droached more nearly 

 to the existing Orthoptera, and perhaps to the wingless 

 Blattidse, than to any other order, and that the " com- 



