494 C. M. Child. 



ends of parts of the old intestine and extend from these regions 

 into the new tissue. In another polyclad I have obtained very 

 strong experimental evidence w^hich I hope to present at another 

 time in favor of the view that the pressure of the intestinal contents 

 upon the walls of the intestine is a factor of great importance in 

 the formation of intestinal branches or the growth of the intes- 

 tine into new parts. The differences in the degree of intestinal 

 regeneration in the pieces now under consideration lend strong 

 support to this interpretation. The difference is not merely in 

 proportion to the difference in size, but in the pieces without 

 ganglia the regeneration of the intestine is relatively less complete 

 than in the others. In consequence of the more powerful and 

 frequent muscular contractions of the pieces with ganglia the 

 intestinal contents are pressed against the closed cut ends of the 

 intestinal branches, or, in later stages, into the extensions of these 

 in the new parts with greater force and frequency than in the 

 pieces without ganglia. It is not difficult to observe this differ- 

 ence. The intestinal branches in the new tissue are much more 

 frequently distended by the contents of the intestine in the pieces 

 with ganglia. Thus in regard to these structures as well as those 

 already discussed the differences in the tissues are, I think, ex- 

 pressions of the differences in functional activity, and especially 

 in this case, of muscular activity. The formative conditions in 

 this case, however, are themselves mechanical. 



As regards the size of the regenerated genital area posterior to 

 the pharynx there are no marked differences in the two sets. Its 

 size remains almost the same in all cases whether the total amount 

 of regeneration is large or small. This uniformity in size is to be 

 interpreted as indicating that conditions which give rise to these 

 organs are wholly or largely independent of the muscular activity. 

 We know little regarding the conditions which may be concerned 

 in the regeneration of these parts, but they are doubtless connected 

 with the presence of other portions of the ducts in the old part and 

 also with certain obscure physiological conditions on which the 

 presence and periodical activity of the sexual organs is also de- 

 pendent. The period at which these experiments were performed 

 was not that of greatest sexual activity; and the organs remained 



