METAMORPHOSIS. 349 



can be regarded as more wonderful than the exuvia- 

 tion of one of these creatures. 



Another important point connected with the history 

 of these Crustaceans is the metamorphosis, which re- 

 cent observations prove them to undergo, preparatory 

 to their assumption of the adult form. Nothing, 

 indeed, can be more dissimilar than the appearance 

 presented by the young crab on first escaping from 

 the egg, and that which, after a few moultings, it 

 subsequently presents ; and few subjects of micro- 

 scopical research are more interesting to the inquiring 

 naturalist than the succession of forms by which this 

 change is progressively effected. 



Mr. Couch procured some of the Shore Crab (Car- 

 cinus Maenas) laden with ripe eggs, just ready for 

 hatching. These were transferred to captivity, placed 

 in separate basins, and supplied with sea- water. In 

 about six hours large numbers of strange-looking 

 animals were seen swimming about with all the 

 activity of young life. There could be little doubt 

 that these creatures were the young of the captive 

 inmates. In order, however, to secure accuracy of 

 result, one of the crabs was removed to another 

 vessel, and supplied with filtered water, that all in- 

 truders might be removed ; but in about half an hour 

 the same creatures were observed swimming about as 

 before. To render the matter still more certain, 

 some of the ova were opened, and the embryo ex- 

 tracted; but shortly afterwards Mr. Couch had the 

 pleasure of witnessing beneath the microscope the 

 natural bursting and escape of one precisely similar 

 in form to those found so abundantly in the water. 



