54 



INVERTEBRATE PHYSIOLOGY 



happened. The number and direction of misses, the number of hits and 

 their bias, that is, whether the prey was hit by the two forelegs or by one 

 only, were noted. Thus we shall characterize the hitting performance by 

 two quantities, first the frequency of misses and the second the left or right 

 tendency calculated from the frequency of biased misses and hits. With 

 regard to the latter quantity it is important to note that, by definition, left 

 tendency plus right tendency always equals 100%. Thus, if right tendency 

 is 100%, left tendency is zero; and if right tendency is 50%, there is no 

 bias at all. ( I should add here that, in calculating the values of some of the 

 diagrams — Figs. 2 and 5 — I have used a different statistical procedure than 

 the usual one. The difference will be less than 1 % if number of strokes is 

 98 or more and thus will be unimportant in most cases.) 



I shall begin with the effects of eliminating the hair plates by nerve 

 section, and shall confine myself to the results of the bilateral total deaffer- 

 entation. In experiments carried out with 5 individuals, the frequency of 

 misses increased from 10-15% in the normals to 70-80% immediately 

 after this operation. There was only a relatively small improvement in 

 the following weeks. On an average, this may be even smaller than in the 

 example shown in Fig. 2, where it is partly due to the chances of an acci- 

 dental bias. If you are watching these animals you gain the impression that 

 they only have a chance to hit flies sitting straight ahead of the prothorax. 



100% 



24 days 



Fig. 2. Result of total proprioceptive deafferentation in two individuals. Ordi- 

 nate : frequency of misses (open circles) and right tendency (solid circles), re- 

 spectively. Abscissa : days after nerve section ; the performance recorded before 

 operation is shown left from the 0-Iine. Thin vertical lines : standard error. 



