on the vision of Arthropods. 395 



there if scarcely anything of the nature of true vision 

 ('* la vision proprement dite doit etre a peu pres nuUe," 

 Part I., p. 28). 



Next he placed Lithobius on the floor of a room lighted 

 at one end, and found that the rule was that the creature 

 walked in lines parallel with the direction of the light, 

 either towards it or away from it. Some moveable 

 obstacles were constructed out of sheets of cork fastened 

 to the end of a stick, so that it was easy to place one of 

 these small walls at any spot in the way of the insect ; 

 where this was done it was found that the Lithohiiis 

 invariably walked against the object till it touched this 

 with its antennae, and this proceeding was repeated even 

 one hundred times in succession. By using instead of 

 the plain cork a piece of white cardboard, a different 

 result was obtained ; if the white cardboard was so 

 illuminated as to form a strong contrast to the floor of 

 the room, then the Lithobius was aware of the presence 

 of the obstacle, and changed its direction so as to pass 

 to one side of it. By using a piece of cork with white 

 paper on one side of it, the other being left of a natural 

 colour, the above results were completely demonstrated ; 

 similar experiments were then made with other colours, 

 the result being that the Lithobius was aware of the 

 presence of an object when much light was reflected 

 from it. 



A similar set of experiments with other Myriopods 

 {Scolo'pendra subspinvpes, Julus londinensis, Glomeris 

 marginata), and also a few other plans for testing their 

 perceptions were employed ; and Professor Plateau thus 

 summarises the results of his observations on Myrio- 

 pods :— 



1. Myriopoda distinguish between light and darkness. 



2. As this capacity exists in blind species, as well as 

 in those possessed of eyes, the perception of light may 

 even in the latter be in part due to dermatoptic sensa- 

 tion. 



3. Myriopods see very badly, and supplement the in- 

 efficiency of their sight by the sense of touch, which is 

 located chiefly in the antennae. 



4. Species possessing eyes are but little better off in 

 vision than those that do not possess eyes. 



5. Myriopods endowed with visual organs perceive the 

 existence of an object placed on their line of route only 



TEANS. ENT. SOC. LOND. 1889. PART III. (oCT.) 2 E 



