THE GEOMETRICAL SNARE 111 



fresh circle to the left. I shall speak of this change 

 in the mode of operation as " the reversal of the 

 spiral." A reference to Fio-. 5 will show two modi- 

 fications of the way in which this reversal is made. 



For a long- time I was at a loss to understand why 

 the spider should suddenly, and without apparent 

 cause, interrupt its instinctive circle and start a reverse 



Fig. 6. — Reversal of spiral in an eccentric snare. 



Points of reversal marked with an asterisk. 



Twelve turns on narrow side, twenty tui ns on broad side of centre. 



spiral in the opposite direction round the snare. It 

 always occurred so unexpectedly and seemed such a 

 very unessential act. It was so complete a change 

 in the undeviating course of instinct, and instinct 

 moves by inexorable laws. 



I noted, however, after examining a number of 

 snares, that what I have called the centre was seldom 

 a true mathematical centre. The radii varied in 

 length, and the centre from where they all diverged 



