No. 503] 



NOTES AND LITERATURE 



751 



lished ten mouths earlier, that single segments regenerate in this 

 way. Although Midler reviews my experiments with single se.tr- 

 ments in full detail, he feels dubious as to whether I really dFd 

 have single segments regenerating. The scepticism is due to the 

 fact that, according to my description, the worms have been re- 

 generating in clean water, and in Miiller's experience "war das 

 Halten der Tiere in reinem Wasser einfach ausgeschlossen. " I 

 may therefore mention in this place that pieces of Lumbrieulus 

 have been reared in clean water even by Bonnet, and that for the 

 three years that I have been studying regeneration in Lumbri- 

 culus the worms were and are now invariably kept in clean 



the parent body, to regenerate new heads or tails 23 times. 



_ The fact that Lumbrieulus can regenerate its head 23 times 

 and its tail 42 times in succession is of considerable theoretical 

 importance, and even more so is the statement that regenerated 

 pieces are also capable of regenerating heads and tails many 

 times in succession. It seems to me that these facts bear di- 

 rectly on the hypothesis of formative substances. If such sub- 

 stances are connected with the regeneration of a head or a tail 

 it would be hard to conceive how such an enormous quantity 

 of head- and tail-forming substances has become stored up in 

 the cells to insure the possibility of regeneration after 23-42 

 operations, unless a further assumption is made that those sub- 

 stances themselves are capable of reproduction. Still harder 

 would it be to conceive how a regenerated tail the supposed 

 product of tail-forming substances, has become stored up with 

 such an abundance of reserve formative substances as to be able 

 to produce heads or tails time after time. To make such a 

 demand on our credulity would be asking a great deal. 



Miiller's work on Tubifex is practically a repetition of his 

 work on Lumbrieulus. There he finds that a head regenerates 

 only when 4-H anterior segments are removed, and does not re- 

 generate more than 7 times in succession, while a tail may regen- 



