CHAP. I. THEIR SENSES. 25 



fetched ; for we thus attribute to the worm 

 attention and some mental power, neverthe- 

 less I can see no reason to doubt the justice 

 of the comparison. 



Although worms cannot be said to possess 

 the power of vision, their sensitiveness to 

 light enables them to distinguish between 

 day and night ; and they thus escape extreme 

 danger from the many diurnal animals which 

 prey on them. Their withdrawal into their 

 burrows during the day appears, however, 

 to have become an habitual action; for 

 worms kept in pots covered by glass-plates, 

 over which sheets of black paper were 

 spread, and placed before a north-east win- 

 dow, remained during the day-time in their 

 burrows and came out every night ; and they 

 continued thus to act for a week. No doubt 

 a little light may have entered between the 

 sheets of glass and the blackened paper ; 

 but we know from the trials with coloured 

 glass, that worms are indifferent to a small 

 amount of light. 



Worms appear to be less sensitive to 

 moderate radiant heat than to a bright light. 

 I judge of this from having held at different 



