lU 



THE GENESIS OF SPECIES. 



[Chap. 



ample of serial homology. The body (except at its two 

 ends) consists of a longitudinal series of similar segments 

 Each segment supports a pair of limbs, and the appendages 

 of all the segments (except as before) are completely alike 

 A less complete case of serial homology is })reseuted by 

 Crustacea (animals of the crab class), notably by the squilla 

 and by the common lobster. In the latter animal we have 



BQUILLA. 



a six-jointed abdomen (the so-called tail), in front of which 

 is a large solid mass (the cephalo-thorax), terminated ante- 

 riorly by a jointed process (the rostrum). On the under 



