362 C. M. Child 



outline of the intestine, and the direction and arrangement of its 

 branches. Lack of nutrition may of course determine the degen- 

 eration of a branch or of branches, but how can the presence ot 

 nutrition determine the position and direction of new branches ? 

 On the other hand, the conditions above mentioned do account 

 readily for position, outline, and arrangement of parts and experi- 

 mental data indicate that they are the factors chiefly involved. 



The development of intestinal branches is simply another illus- 

 tration of the fact which I have mentioned elsewhere at various 

 times, viz: that the stimulus to growth is not identical with the 

 presence of nutritive material, but that, on the other hand, nutri- 

 tive material goes where the demand is greatest even at the 

 expense of reduction and disappearance of other parts where the 

 demand is less. This relation between growth and nutrition 

 seems also to show why such extensive intestinal reduction occurs 

 in many turbellaria during starvation: the demand for nutritive 

 material is greater in other parts than m the mtestme, consequently 

 material passes from it to them. In short, I believe the whole 

 problem of the "self-regulation of metabolism" durmg starvation 

 and indeed at other times is essentially a problem of relative func- 

 tional activity in the broadest sense. 



In Cestoplana the axial intestine extends directly through the 

 median region of the body from end to end. The lateral branches 

 are at right angles to the axial intestine in the pharyngeal region, 

 but toward the anterior end gradually change their direction, and 

 are directed more and more anteriorly: posterior to the pharynx 

 exactly the reverse is the case (Fig. i). 



The movements of intestinal contents in this species are briefly 

 as follows: general contraction of the body forces the intestinal 

 contents from both ends toward the pharyngeal region, and the 

 axial intestine and the lateral branches of the middle region of 

 the body become distended. General extension of the bodv 

 forces the intestinal contents out of the middle region to a large 

 extent and distributes them along the lateral branches even to 

 the extreme terminal regions, if the contraction is strong. 



Under these conditions the intestinal contents move anteriorly 

 in the prepharyngeal and posteriorly in the postpharyngeal region. 



