RETREAT 375 



a large piece of its body, if bitten off, can be renewed. And cases 

 must frequently occur where the front end of such a creature 

 manages to make its escape while the pursuer is devouring the 

 piece which he has captured. It has been plausibly suggested 

 that segmentation of the body, in its first origin, was evolved 

 as a defensive measure. A lower form constructed in this way 

 consists of a series of rings or segments, sometimes extremely 

 numerous, each of which contains a portion of most of the organs, 

 digestive, excretory, nervous, &c., so that even the loss of a con- 

 siderable number of segments leaves the animal sufficiently well 

 provided in these respects to carry on its existence till the wound 

 is healed and the parts destroyed have grown once more. In the 

 higher segmented forms (Arthropods, Vertebrates) the body has 

 become so specialized that this mode of defence has been mostly 

 or entirely given up, though even in so highly developed an 

 animal as a Lizard the part which can be relinquished and re- 

 newed, i.e. the tail, is made up of the posterior segments of the 

 body. 



