126 



Herbert Eugene Walter 



This marked difference in behavior might possibly be explained 

 on the hypothesis that the direct effect of light on the deeper lying 

 nervous system is inhibitive; that is, so excessive as to produce a 

 sort of light rigor. Thus the more the central nervous system is 

 shielded from light by pigment the less the inhibitive effect becomes 

 apparent. Certain it is that Bdelloura Candida, which has dark 



TABLE XXXIV 



The behavior of dark-pi gmented worms contrasted with that of worms not possessing dark pigment dis- 

 tributed over the body. The number of observations in each case is not given since the details of this 

 table have already appeared elsewhere 



Duration of movement in a typ- 

 ical set of experiments, minutes 



Percentage of orientation to light 

 upon coming to rest 



Wigwag responses at the critical 

 line separating two intensities 

 of non-directive light, per cent 



Average number of seconds re- 

 quired to escape from a circle 

 10 cm. in diameter 



Precision of response 



Deviation in degrees upon emerg- 

 ing from a circle 10 cm. in dia- 

 meter when headed away from 

 the light 



Rate of locomotion in mm. per 

 sec 



Dark pigmented 



■3 c8 &, 



K 6 



47 



24.4 

 i-47 



60 + 

 4i 



39 



59-6 



2 5-3 

 1.075 



60+ 



39-6 



29.1 

 J-395 



56 + 

 41 



39 



49-3 



26.3 

 1.28 



Light pigmented 



3° 



8-5 



62.2 



0.85 



'5 



27.6 



11. 4 



16 + 

 30 



44-9 



10.7 

 0.85 



pigment in its eyes only, may be brought to a standstill very read- 

 ily by means of light stimulation. With the exception of the eyes 

 it may be possible that the photoreceptive apparatus is not differ- 

 entiated to such an extent that it could fairly be said that any part 

 of the translucent planarian body is entirely free from the direct 

 stimulation of light. The relation of pigment to light reactions 



