CHANGE OF SHAPE IN PLANARIA. 



279 



a 



...b 



I. EXPERIMENTAL DATA. 



When whole individuals or pieces are placed in 1.5 per cent, 

 alcohol or in 0.4-0.5 per cent, ether they lose the power of coor- 

 dinated movement almost entirely for a time. After four to five 

 days, however, they become in some degree acclimated to the 

 new conditions and begin to move about very slowly, but with 

 increasing vigor as time goes on, though they never attain the 

 normal motor activity. Pieces including the old 

 head begin to move about earlier than pieces with- 

 out a head, for the latter must form a new head be- 

 fore they can regain the usual degree of motor 

 activity, and regulation is greatly delayed in the 

 solution. The important point for the present pur- 

 pose is that for some days movement, and particu- 

 larly coordinated locomotion, is almost completely 

 eliminated. It is of interest to determine to what 

 extent regulation occurs under these conditions. 



The first experiment to be described concerns 

 pieces including that part of the body anterior to the 

 line b in Fig. I, /'. e., short pieces with the old heads. 

 In Fig. 2 a piece of this kind after ten days in 1.5 

 per cent, alcohol is shown : during this time the 

 piece has moved about but little and that chiefly 

 during the last few days. Fig. 6 represents a 

 similar piece after five days in water, Fig. 7 the 

 same piece after ten days. Comparison of Figs. 2 

 and 7 shows that regulation in the alcohol is 

 greatly delayed : a little new tissue has been formed 

 at the posterior end, but, as a microscopic examina- 

 tion under pressure shows, it is still a mass of cells 

 without any marked visible differentiation, and it 

 can readily be seen that it is not used as a tail and 

 is not attached to the substratum as the animal 

 creeps slowly about ; a small group of cells is 

 present in the pharyngeal region, but these likewise show no 

 marked differentiation. In water, on the other hand, a new 

 tail has been formed which functions in the normal manner, con- 

 tracting, extending and attaching to the substratum as the animal 



FIG. i. 



