KEGENERATION 11 



of regeneration is still very limited, for at most two worms, and 

 sometimes only one, can develop from an animal cut into two 

 pieces. Cutting into a greater number of pieces does not yield 

 a larger number of worms, but usually only one, and often none 

 at all. 



This corresponds to the behaviour of their enemies, which may 

 often bite off a piece or tear it away when the worm attempts to 

 escape, but never cut it up into pieces. The regenerative capacity 

 is more highly developed in the genus AUurus, more highly still 

 in the worms of the genus Criodrilus which lives in the mud at 

 the bottom of lakes, and most highly of all in the genus Lumbriculus 

 which lives at the bottom of small ponds. Long ago Bonnet cut up 

 a specimen of Lumbriculus into twenty-six pieces, of about two 

 millimetres in length, and he observed most of these grow to complete 

 worms again. His experiments have often been repeated in recent 

 times, and have been extended and made more precise in many ways. 

 Von Biilow was able to get whole animals from pieces consisting of 

 from four to five somatic segments, and with eight or nine segments 

 he almost invariably succeeded. A Lumbriculus which he had cut 

 into fourteen pieces, one of which only measured g'^ mm. in length, 

 gave rise to thirteen complete worms with head and tail ; only one 

 piece perished. 



These worms have little enemies with sharp jaws which may 

 gnaw at them behind or before but cannot swallow them whole. 

 Lyonet, famous for his analytic dissection of the wood-caterpillar 

 (Cossus ligniperda), observed when he was feeding the larvse ' of 

 dragon-flies with these Lumbrieulid worms that 'the anterior end 

 of some whose posterior end had been gnawed away by the larvse 

 continued to live on the ground.' We can thus understand why 

 a high power of regeneration is of use to these worms, and at the 

 same time why it is advantageous to them to contract so that 

 they break in pieces on very slight irritation, but to this we shall 

 refer again. 



The very diverse potency of the faculty of regeneration in 

 animals belonging to the same small group, and nearly, if not quite, 

 at the same level of organization, seems to show clearly that we 

 have here to do with adaptation to different conditions of life, 

 although we cannot demonstrate this in detail. It would certainly 

 be erroneous to regard the conditions of life as uniform, since the 

 worms in question not only live in different places — in the earth, 

 in mud, or in water — and are thus exposed to different enemies, and 

 since they may also be quite different in regard to size and speed, 



Digitized by Microsoft® 



