child] form-regulation in ccelentera and turbellaria 135 



with the same rapidity as pieces containing the gangha. It is evi- 

 dent therefore, that there is no direct relation between the presence 

 of the cephaHc ganglia and regeneration in general, the presence of 

 the ganglia being necessary merely for the regeneration of the head. 



During the course of regeneration the form of both the new tissue 

 and the old parts becomes more or less altered. In specimens with- 

 out food there is of course a reduction in size, but in addition to this 

 the pieces become relatively longer and more slender (" morphal- 

 laxis," Morgan). An extended study of these phenomena was made 

 and distinct confirmation of the conclusions reached in regard to 

 Stenostoma was obtained, viz., that this change in form is due pri- 

 marily to the tension to which the tissues are subjected by the move- 

 ments of the animal, and especially by the antagonism between 

 attachment to the substratum by the posterior end and the force of 

 the forward movement in consequence of muscular or ciliary activity. 

 The rapidity of this change in proportion depends on the degree of 

 activity of the individual, the rapidity and frequency with which it 

 moves about, and consequently the longitudinal tension to which its 

 tissues are subjected. One case serves as an illustration: Pieces de- 

 prived of the cephalic ganglia are incapable of carrying out the 

 topical creeping movements ; they are able to advance very slowly 

 after strong stimulation, but remain quiet most of the time when un- 

 disturbed. As was noted above, absence of the cephalic ganglia does 

 not directly affect regeneration at the posterior end of a piece. With 

 these two facts in mind, two sets of pieces were prepared, the pos- 

 terior ends of all pieces representing the same level (anterior to the 

 middle) of the body. From one set heads and cephalic ganglia 

 were removed ; the other set retained these organs uninjured. The 

 pieces of the latter set moved about actively, those of the former 

 showed scarcely any power of movement. In the latter set the 

 bodies, and especially the plastic regenerated tissue, gradually 

 assumed a tapering form with greatest breadth at the anterior end 

 and pointed posteriorly. The pieces of the set without cephalic 

 ganglia regenerated from the posterior cut surface, but the new 

 tissue grew out in a rounded mass and neither new nor old tissue 

 ever acquired a tapering form. Various other methods of attacking 

 the problem were employed, and all with the same result. 



It was found that pieces of a certain shape would move in circles 

 after the extensive contraction of the cut surface had taken place, 

 this movement being due to the one-sided effect of the cilia. In such 

 pieces the regeneration occurred as usual from the posterior cut sur- 

 face ; the new tissue, however, did not grow out in the direction of 



