The Reactions of Planarians to Light 



99 



data there used are rearranged for the present purpose in Table 

 XIX. , 



TABLE XTX 



Percentage of generic and specific negativeness in worms started at right angles to incident light, as deter- 

 mined at the circumference of a circle 10 cm. in diam. by the average amount of their deviation from 

 the directions in which they were started 





Generic differences 



Specific 

 differences 





Dendro- 

 coelum 



Phago- 

 cata 



Planaria j Bdelloura 



Planaria 

 maculata 



Planaria 



gono- 



cephala 





78 



155 

 2112 

 93.1 



80 



238 



1964 



89.6 



ic8 10 



78 



5 

 2102 



99-9 



80 



Total number of degrees positive.. . 

 Total number of degrees negative. . 

 Percentage of negativeness 



165 

 4070 

 96.1 



397 



5° 

 11 



160 

 1968 

 84.6 



Comparing the figures given in this table, a greater range of 

 difference is seen to obtain between the two species of Planaria 

 (P. maculata and P. gonocephala) than between the genus Planaria 

 and either of the other negative genera, namely, Dendroccelum and 

 Phagocata. Although not indicated in this table, similar results 

 appear when the number of times the worms went in a negative 

 direction is used as a basis of comparison, instead of the total num- 

 ber of degrees of negative deviation. 



Character of the Course in Directive Light. When worms were 

 placed on the middle of a rectangular aquarium floor and sub- 

 jected to a directive light their movements showed both generic 

 and specific differences. By experimenting with one worm at a 

 time it was possible to plot on a sheet of paper with sufficient 

 accuracy for general comparison the entire course of the worm 

 during a considerable period. This was done many times and 

 typical records of such observations are given in Figs. 10-14. In 

 such instances the worm was exposed to a light of approximately 

 147 cm., placed so as to correspond to the right side of the 

 figures. The central rectangular area bounded by the broken lines 

 indicates the limits of the floor of the aquarium, while the smaller 

 exterior adjacent areas represent its vertical sides so rotated as to 



