474 C. M. Child. 



the ganglia the less the activity and the more irregular and im- 

 perfect are the movements. The difference between a piece ob- 

 tained by a cut just posterior to the ganglia and one from the 

 region posterior to the pharynx is striking. The latter scarcely 

 reacts at all to stimuli, is almost v^holly incapable of progressive 

 locomotion and rarely succeeds in righting itself — though this 

 last may be due in part to the fact that such pieces are necessarily 

 short— while the activity of the former is much greater in all 

 respects though far below that of the normal animal. 



So far as I am aware the case of Dendroccelum mentioned by 

 Lillie ('oi) is the only one in which observations of this kind have 

 been made. In Detidroccelum Lillie found that posterior pieces 

 obtained by section in the anterior third or fourth of the animal 

 reacted to light like normal animals though more slowly, while 

 pieces from levels posterior to this did not react. He does not 

 mention any degree of reactive power corresponding to difference 

 of level of the cut in pieces capable of reacting, but since other 

 Turbellaria which I have observed resemble Leptoplana more or 

 less closely, I am inclined to think that such a difference may 

 possibly be present, though I have not had the opportunity of 

 examining Dendrocoelum in sufficient numbers to decide this 

 point. 



The differences in pieces from different levels are not due simply 

 to differences in size, for a short piece from the region just pos- 

 terior to the cephalic ganglia is much more active than a piece of 

 the same size from the posterior region.- It is apparently not 

 simply the amount of nerve tissue present that determines the 

 degree of motor activity, but rather the quality of this tissue which 

 differs in different regions. With our present knowledge of the 

 nervous system only vague surmises as to the nature of this differ- 

 ence are possible. It may be, at least in part, a difference in 

 structural complexity, or the difference in the quantity of energy 

 transformed by the stimuli or it may be something different from 

 either of these: as a matter of fact the nerve cords in the Turbel- 

 laria diminish in size toward the posterior end of the body. But 

 the fact that a difference exists is important. My observations 

 also indicate that the case is somewhat similar as regards the ceph- 



