182 



THE GENESIS OF SPECIES. 



[CHAP. 



mentally the same, for all these appendages are modifica- 

 tions of one common kind of structure, which "becomes 

 differently modified in different situations ; in other words, 

 they are serial homologues. 



SQUILLA. 



The segments of the body, as they follow one behind 

 the other, are also serially alike, as is plainly seen in the 

 abdomen or tail. In the cephalo-tliorax of the lobster, 

 however, this is disguised. It is therefore very interesting 



