56 



INVERTEBRATE PHYSIOLOGY 



large decrease in hitting performance but also a strong bias, namely, a fre- 

 quency of misses and a right tendency of 80-90% within 24 hours after 

 operation on the left side. The experimentals were first tested with the 

 head fastened only, and then operated unilaterally leaving the balsa bridge 

 intact. The result is seen in Fig. 4. There is an effect of the additional op- 

 eration and in the same direction as in the controls. The effects of the con- 

 stant head deviation and of the unilateral nerve section are clearly super- 

 posed. The relative importance of the components can be estimated from 

 the fact that the bias caused by eliminating one-half of the proprioceptors 

 is completely compensated for by a mean head deviation of less than 20° 

 (see left column of Fig. 4). 



r- tendency 

 caused by fixaiion 



r- tendency 

 faults 



of sirokes 

 of animals 



20 -i07o 



before op. after 



30,7 -^(^ 



i3V — 1,6,8] 



202 156 



4 



-50 7o 



before op. after 



50,0-^(78)) 

 23,^^718 



175 UL 



60-80 7o 



before op after 

 (62,5 — 95,0) 



197 



60 



Fig. 4. Result of head fixation combined with unilateral proprioceptive deafferen- 

 tation classified into three groups according to the bias caused by head fastening only. 

 A right tendency of 20-40% (left column) corresponds to a mean head deviation of 

 <20° to the right ; an r-tendency of 50% corresponds to the median head position ; an 

 r-tendency of 60-80% corresponds to a mean head deviation of <20° to the left. The 

 mean values obtained with head fastening alone are shown under "before op.," those 

 obtained within 24 hours after an additional section of the left nerve under "after." 

 Left nerve section without head fixation (controls — not shown in the table) causes 

 a frequency of misses and a right tendency of 80-90%. 



In the fourth and last set of this series I loaded the head of the other- 

 wise undisturbed animal by an extraneous mechanical force. A small stick 

 of balsa wood was gummed on the posterior wall of the head and then a 

 small ball of plasticine of known weight was fastened on the stick at a 

 distance of about 10 mm. Of course the animals had to be tested sitting 

 on the vertical wall of their cage and even then we only counted the strokes 

 executed while the prothorax had a vertical position. 



