CRUSTACEANS. 
481 
of natation which they have hitherto possessed. After this they are 
no longer able to maintain themselves on the surface, but drop to the 
bottom. Henceforth they are condemned to remain there, and such 
walking as they can exercise becomes their habitual mode of progres- 
Sl °n. As they increase in size they gradually approach the shore, 
ybich they had for the moment abandoned, and return to the places 
nfhabited by the parent Crustaceans. 
The form of the larvae differs so much from that of the adult, that 
