338 Journal of Comparative Neurology and Psychology. 



reflexes are no longer performed in certain conditions of the 

 nervous system. 



The swaying movements of the body in response to changes 

 in the position of the Hght seem almost as mechanical as the 

 head reflexes. They are more easily inhibited, however, since 

 they are often checked by efforts to rub the eyes, to clean the 

 body, or to raise the wings after they have been fastened down, 

 but they are immediately resumed as soon as the energies of the 

 insect are no longer diverted to other actions. The swaying 

 movements of the body are the result of a strong and definitely 

 directed tendency to action which, when the insect is in a cer- 

 tain condition of tonus, it seems powerless to control. It is only 

 when other instinctive responses are brought into play that the 

 insect is able to overcome its phototactic activities. 



The swaying movements of the insect vary, however, 

 according as it reacts to light in a positive or a negative manner, 

 but there is little evidence of choice as regards which mode of 

 response is followed. In one nervous condition the insect is 

 always negative ; in another condition it is always positive. A 

 Ranatra that is lethargic and sluggish reacts to light in a nega- 

 tive manner, while one that is highly wrought up and excited is 

 always strongly positive. In intermediate states of excitement 

 there is often a hesitation between the two modes of response, 

 and the insect may exhibit alternate fits of positive and negative 

 phototaxis of short duration. The power of one instinctive 

 response to inhibit or overcome another may be considered as 

 the first step towards the voluntary control. Choice as mani- 

 fested by Ranatra is determined by which of two instinctive ten- 

 dencies to action gains ascendency. 



The mechanical nature of the phototactic response is further 

 evinced by the effect of blackening over different parts of the 

 eyes. When the posterior sides receive light the legs are ex- 

 tended and the anterior part of the head and body are held high 

 in the air. When only the anterior sides receive light the head 

 and body are bowed down. If light comes in only at the side 

 of one eye the legs are flexed on the side towards the Hght and 

 extended on the side away from it. It would almost seem as 



