162 Mr. H. M. Bernard on 



in spirit they at once seize one another and form themselves 

 up into a complete mass, which is tightly held together by 

 the mandibles. 



The " soldier" of Atta cephalotes is the same in form in 

 Nicaragua as in Trinidad, and possesses the same powers of 

 defence and offence. 



Trinidad, 

 January 9, 1896. 



XXTV. — The Sense of Sight: Sketch of a new Theory. 

 By H. M. Bernard, M.A. Cantab., F.L.S., F.Z.S. 



FOR nearly ten years I have been engaged in endeavouring 

 to find an explanation of light sensations. I have at last 

 worked out a theory capable of connecting and explaining 

 most of the phenomena, and, what is still more important, 

 apparently capable of demonstration. I am now engaged in 

 arranging the evidence ; but in the meantime I am urged to 

 publish a short abstract of the conclusions arrived at, because, 

 in the first place, the duties which I have undertaken at the 

 Natural History Museum must necessarily retard the publica- 

 tion of a fuller treatise, and, in the second place, because, the 

 subject being one of wide interest, physiologists and zoologists 

 will have an opportunity of recording observations either for 

 or against the theory, .which will be useful towards the 

 ultimate solution of this important problem. 



In the following pages I propose to confine myself solely to 

 a statement of my own theory, abstaining entirely from all 

 criticism, and even from all mention of existing theories, 

 except when the subject requires it. 



A long series of observations on different Metazoa, ranging 

 from the Platodes to the Vertebrates *, have convinced me 

 not only that wandering-cells, apparently acting as scavengers 

 among the tissues, collect granules discharged from other cells 

 or matter to be afterwards formed into granules, but that the 

 importance of this process is not exclusively physiological. 

 These granules are conveyed by the wandering-cells to organs 

 which lead out of the body, where they may be put to 

 secondary uses. The granules themselves not only differ 

 greatly in different animals, but may also differ in one and 

 the same animal. The secondary utilization of these granules 

 takes place, in many cases at least, by their transference from 



* Nat including, however, the Echinoderms ; and on these cf. Mr. H. 

 Durham's paper in the ' Quarterly Journal of Microscopical Science,' 

 vol. xxxiii. p. 81. 



