VARIATION. 271 



Observations. — The worms were kept for observation in a box 

 two feet square by one foot deep, one side of which, a, b, c, d, 

 was of glass. This box was nearly filled with vegetable mould, 

 sifted so as to be of fine tex- 

 ture, and fairly well dried, in 

 order to facilitate penetration 

 in burrowing by the worm. 



The following, briefly, are 

 the facts observed : — 



(1) On being placed on the 

 surface of the soil near the glass side, and a cloth placed over 

 the glass, it was seen, by the removal of the cloth from time to 

 time, that the worm burrowed by keeping the lesser head in a 

 retracted condition, and alternately expanding and retracting 

 the larger head, thus penetrating the soil after the manner of 

 the normal individual of the same species. The path, however, 

 always took the form of a curve in the direction of the larger 

 head, owing, no doubt, to the slightly increased irritation of 



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Path of Burrow 





the smaller head causing a deflection in the opposite direction, 

 being an attempt to lessen the irritation. This seemed decidedly 

 the case, for whenever the smaller head came against the smooth 

 glass (therefore, no appreciable friction and irritation) the path 

 took the normal irregular direction. 



(2) When the glass side was uncovered, the burrowing ceased 

 and was not resumed until darkness again prevailed. The head 

 part was much more sensitive to light than the hinder end. 



(3) Sounds seemed to affect the worm to no appreciable extent. 



