44 SOCIAL LIFE IN THE INSECT WORLD 



The sight of an insect is in one sense poor — it consists of a kind of 

 mosaic picture, and for one insect to distinguish another clearly the 

 distance between them must not be very great. Certain gregarious 

 birds and fish whose colouring is protective have a habit of showing 

 their white bellies as they swerve on changing their direction. 

 These signals help to keep the flock together. The white scut of 

 the rabbit and of certain deer is a signal for other deer or rabbits to 

 follow a frightened flock. It is obviously to the advantage of the 

 Cigale to follow a gregarious habit, if only for purposes of propaga- 

 tion, for this would be facilitated by the sexes keeping together, 

 and, deaf or otherwise, the vibrations of its cry would enable it to 

 do so. It would be easy to show a priori that the perception of 

 such vibrations must cause the insect pleasure, as they stimulate a 

 nervous structure attuned to the perception or capable of the pro- 

 duction of certain complex vibrations. The discord of the cry is 

 caused by the fact that it consists of a number of vibrations of 

 different pitch. Some would set the contents of the male resonating 

 cavities in vibration ; others would affect the less regular cavities 

 in the thorax of the female. We might compare the Cigale's cry to 

 a sheep-bell. That it is felt and not heard explains its loudness and 

 its grating quality. A Cigale with the resonating cavities destroyed 

 would possibly be lost. The experiment is worth trying. — [Trans.1 



