300 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 1 37 



the sweep circuit of a cathode-ray oscilloscope having a long-per- 

 sistence screen. Contact with the fly generated a pulse in the second 

 pickup which was displayed on the oscilloscope as a vertical deflection. 

 The position of this pulse on the timed sweep was measured directly 

 from the tube face. Owing to caprices of mantis appetite, double 

 strikes, and the general unpredictability of the action, only five clear- 

 cut strike times were obtained from a number of strikes. These were 

 48, 51, 58, 62, and 75 msec. It is interesting to note that these strike 

 times correspond quite closely to the startle times of potential prey 

 recorded in the previous section. 



The complex part of this feeding behavior consists of the opera- 

 tions which steer and release the strike. Mittelstaedt has shown that 

 direction is determined by a combination of visual and proprioceptive 

 information. Upon detection of the prey the mantis turns its head 

 in this direction. When the prey is in any position other than directly 

 in front of the mantis this head movement does not bring the prey 

 completely into the visual fixation line. This happens because increas- 

 ing asymmetry of the nerve discharge from proprioceptive hairs on 

 the right and left cervical sclerites tends to restore the head to its 

 resting straight-ahead position with respect to the prothorax. This 

 fixation deficit is small but constant, and is proportional to the angle 

 by which the head deviates on the prothorax in turning toward the 

 prey. In a number of ingenious experiments Mittelstaedt (1954, 1957) 

 has shown that movements of the head in following the prey are 

 steered by the difference between the optic center message (the neural 

 equivalent of the slight optic asymmetry expressed by the fixation 

 deficit) and the proprioceptive center message (the neural equivalent 

 of asymmetric stimulation of the neck proprioceptors). At the moment 

 of attack this information determines the direction of the strike. 



From this it appears that the stage of taking aim depends upon 

 complex and relatively time-consuming processes. Fine quantitative 

 discrimination from two or more sensory systems must be centrally 

 integrated before the direction of the final attack is determined. The 

 compound eyes of the mantis, the primary sense organ in this opera- 

 tion, consist of many thousands of ommatidia connected to the nervous 

 system by a large number of very short nerve fibers. The complexity 

 of the optic ganglia, to which these fibers pass, has so far prohibited 

 any analysis of the central representation of the visual sense. Simi- 

 larly, the cervical hair plates each contain several hundred tactile sen- 

 silla, and the fibers running from them to the prothoracic ganglion 

 must be of small diameter. The direct tracing of the nerve pathways 



