Some PlK'UOiiuna uf Regoiuraiiüu in Limiiodrilu.s and iclatwl Foniis. 429 



the coelom assunie a serrated appearance. That a cell sliould siniul- 

 taneously act as an epidermal cell and a muscle forming cell as well 

 is rather remarkable in animals so highly organized as are those under 

 consideration. It is cortainly a most primitive condition and as Nüss- 

 baum says it reminds oiie of the conditions found in the coelenterates. 



Before leaving this discussion of the normal regenerative phe- 

 nomena one or two points might be touched upon that have not yet 

 been considered. With regard to the supply of neoblasts which form 

 the various mesodermal organs at the posterior end of a regenerating 

 worm Iwanow is of the opinion that the neoblasts are constantly 

 being renewed while on the other liand Randolph believes that the 

 neoblasts wliicli reach the wound soon after the body has been severed 

 form all the subsequent mesoderm. Neither gives any particular evi- 

 dence in support of the view held. The results of my own observations 

 are not entirely satisfactory but still they may shed some light on the 

 question. If the supply of neoblasts is constantly being renewed the 

 neoblasts sliould be migrating as long as the posterior end of the worm 

 continues to grow. In worms of about normal length that were exa- 

 mined no neoblasts were seen migrating altliough a group of them 

 was at the extreme posterior end of the body. In individuals in which 

 regeneration from the posterior end of the body had not proceeded 

 very far some neoblasts were apparently migrating. It seems probably 

 therefore that neoblasts continue to migrate as long as new mesoderm 

 is being formed. Because neoblasts were not seen to be migrating in 

 the individuals of normal length does not necessarily iniply that they. 

 entirely cease to migrate in such individuals. So far as we know the 

 species of worm being considered in this paper never cease to add new 

 somites at the posterior end of the body but an individual of the length 

 normally found can be safely assumed to add new somites at a much 

 slower rate than would one which has not yet reached this length and 

 therefore it is probable that in the individual of normal length the 

 demand for neoblasts is not so great as in the other individual and 

 consequently it is also probable that a new neoblast migrates to the 

 posterior end of the body only occasionally. 



Various groups of ceUs under various names have been described 

 by some authors as occurring in both the ectoderm and the neoblasts. 

 In the ectoderm Randolph mentions five "foundations" or groups of 

 cells on each side of the median plane of which the midvcntral pair 

 form the ventral nerve cord and the others, according to their position, 

 the dorsal and the ventral setae and the lateral-line nerve. Janda (02) 



