i.J GENERAL VIEW. u 



riimana has inexactly been applied to the apes, the foot 

 having so close a superficial resemblance to the hand. 

 Parts which answer to each other in serial symmetry are 

 termed " homotypes? 



An amount of serial symmetry, however, far beyond any- 

 thing which man presents is developed in the sub-kingdom 

 Annulosa, as we may see in such creatures as the lobster. 

 Not only is there in such animals an obvious serial repeti- 

 tion in similar segments and similarly formed limbs, but a 

 little study shows that parts superficially unlike (as the 

 feelers, or antennse, jaws, claws, legs, and swimmerets) are 

 essentially similar structures, diversely modified to meet 

 diverse requirements. 



The maximum of serial repetition, however, is found in the 

 hundred-legs and thousand-legs and 

 other Annulosa, in which the num- 

 ber of body segments is at its 

 maximum. 



14. The possession of a solid in- 

 ternal frame-work to which muscles FJG. 12. A CENTIPEDE, OK 

 are attached is a character man HUNDRED-LEGS (Scoiopemtra). 

 shares with all the members of the 



Vertebrate sub-kingdom ; buf quite other conditions may 

 obtain and indeed numerically preponderate, as in the vast 

 group of Annulose animals, where the hard parts are external, 

 and the muscles which move them are within them and 

 attached to their inner surfaces, as familiarly known to us 

 in the lobster. 



15. A permanent mouth may seem to many to be an organ 

 necessary to every animal. This, however, is not the case, 

 as animals so complexly organized as the tapeworm are alto- 

 gether destitute of any such structure and feed by absorption 

 only. Even certain minute creatures which swim freely 

 about to seek their food may yet have no permanent mouths, 

 but (as, e.g., Amoeba and Protogenes) when in contact with 

 their food may produce a temporary perforation in the sur- 

 face of their own body in which they engulph their food, the 

 body-wall closing up again over it. 



It becomes, then, hardly necessary to say that an alimen- 

 tary tube is not a constant structure, still less any inferior 

 outlet ; for many animals, e.g. the lamp- shell (Terebratuld], 

 though possessing an intestine, are nevertheless aproctous. 1 



The various organs which aid digestion disappear as we 



1 From u, not, and irpuK-rof, anus. 



