THE METAMORPHOSES OF CRUSTACEA 87 



past, all the diverse branches of the Crustacean 

 class took their origin. There are, however, con- 

 siderable difficulties in the way of this view. That 

 some such ancestral type did exist may be regarded 

 as tolerably certain ; that it resembled in its adult 

 state the nauplius larvae of present-day Crustacea 

 is, on the whole, unlikely ; but it is not at all 

 improbable, whatever its adult structure may have 

 been, that it hatched from the egg as a nauplius 

 larva. 



With regard to some of the other larval forms, 

 it is possible to speak with a little more confidence. 

 There are good grounds for believing, apart from the 

 evidence of development, that the Lobster and its 

 allies have descended from Crustacea which, like the 

 existing Euphausiacea, possessed swimming branches 

 (exopodites) on the thoracic legs ; and there seems 

 no reason to doubt that the " schizopod " larva of 

 the Lobster does recapitulate this stage in the evolu- 

 tion of the race. On the other hand, it is impossible 

 to believe that any of the ancestors of the Shore 

 Crab resembled, even remotely, the zoea stage with 

 which the life-history of the individual now begins. 



