x REGENERATION OF LOST PARTS 283 



at the penultimate segment, is due to activity in a segment (any 

 segment) further forwards ; in other words, in the less modified 

 worms every segment has the power of forming new tissues, just 

 as each of the joints of a crab's leg has the power of forming 

 the remaining joints when injured. It is not therefore surpris- 

 ing that a " zone of budding " arises in an uninjured worm at 

 certain seasons, viz. that of reproduction ; it is a property that 

 each worm possesses, though generally it remains latent till 

 injury provides the stimulus. 



Moreover, not only can new segments arise at the hinder end, 

 but a new head can be formed at the anterior end, as has been 

 observed in worms belonging to many families in the less modi- 

 fied Syllidae, 1 in others of the Nereidiformia, and even in 

 Sabellids, where the greatly specialised gill filaments can be 

 reproduced. Thus Sir J. Dalyell 2 noted in Dasychone that the 

 crown of branchiae was regenerated in about a month in spring- 

 time, while in winter the process occupied 116 days. He cut a 

 Dasychone into three pieces ; the hindermost produced a head, 

 the anterior piece developed an anus, and the middle portion 

 formed both a head and tail ! 



These regenerated heads are of course at first smaller than the 

 rest of the body, but soon grow to a normal size. Naturally 

 this extensive power of regeneration is of extreme value to the 

 Polychaetes, for if a fish or other enemy bites the head off a 

 worm, a new one can form ; and it is not difficult to see in this 

 the origin of the reproduction by fission as a normal process. 



1 Two new heads have been observed in Typosyllis varicgata by Langerhans, and 

 two new tails in another Syllis. 



* Dalyell, The Powers of tJie Creator revealed, etc., vol. ii. 1853, p. 225 et seq. 



