210 



CHAPTERS ON EVOLUTION'. 



Lake; the Fairy Shrimps, which, like Crustacean ghosts, flit through 

 our fresh waters ; or the curious Apus, with its sixty pairs of feet, begin 

 life each as a Nauplius (Fig. 128, ), bearing either two, or the statutory 

 three pairs of limbs. And the account of other Crustaceans in which 



FIG. 125. TRILOBITES. 



(as in the woodlice -tribe) the Nauplius- stage is passed either within 

 the egg or is altogether suppressed, might similarly bring again before 

 our mental view the operation of the laws and principle of modification. 

 It may, however, suffice, if, in drawing Crustacean history to a 

 close, we select a few examples of development from the highest and 

 most specialised group of the class that of the Crabs, Shrimps, 



FIG. 126. 



LARVAE OF KING CRAB AND TRILOBITE. 



FIG. 127. 



Prawns, &c. In such a history, we may discover the important fact 

 that, notwithstanding modification, and despite the high specialisation 

 of these latter animals from the primitive types and root-stock of 

 Crustacea, their community of descent with that of all other members 

 of the class is proved by those clues and traces, which, all-insignificant 

 as they may appear to the ordinary observer, literally afford to the 

 zoologist proofs and confirmations of the strongest character of the 

 truth of the theory of descent. 



The higher Crustaceans (or Decapoda, as they are called), includ- 



