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C. M. CHILL). 



the pieces described above. The reduction of collapsed pieces 

 has been mentioned several times in this series of papers (see 

 especially '04$) and need not be discussed in detail again. The 

 fact that the relation between length and transverse diameter 

 changes in opposite directions in collapsed and distended pieces 

 is important and may, I think, be taken to indicate that the dis- 

 tention with water plays some part, either directly or indirectly, 

 in the " elongation " which distended pieces undergo. Two 

 possibilities suggest themselves to me in this connection, viz. : 

 either the pressure of the water in the enteron constitutes in 

 some way a stimulus to elongation or the change of form is an 



10 



1 1 



12 



incidental result of the behavior which is markedly different in 

 distended and collapsed pieces. 



Regarding the first of these possibilities, viz., internal pressure 

 as a stimulus to elongation I can offer no experimental evidence. 

 I desire merely to call attention to certain points. It is evident 

 that the general internal pressure cannot constitute a stimulus to 

 elongation unless we postulate a difference in the reactive capacity 

 of the tissues in different directions ; it may be that such a differ- 

 ence exists but I know of no basis of fact for this assumption. 

 On the other hand it is possible that currents in the enteron 

 might exert local pressure in particular directions. It has already 

 been noted in numerous cases (Child, '04/7, '04^, '04^, '04^, '05) 

 that there is some ground for the belief that circulatory currents 

 (Child, '04^) may constitute factors in the localization of regener- 

 ation, /. c., that the local pressure may act as a stimulus to. 

 growth. Currents passing orally along the inner surface of the 

 body wall in all the intermesenterial chambers must produce a 



