LATERAL AND CENTRAL EYES OF SCORPIO AND LTMULUS. 185 



said to be at present properly understood. It is perfectly 

 certain that in some eyes, and possibly in all, pigment does not 

 play a primary part in the physiological process set going by 

 light. Light acts with full effect upon transparent protoplasm, 

 and no pigment is necessary, converting the energy of light 

 into the energy of heat, in order that the protoplasm of cells 

 may constitute an apparatus sensitive to light. The function 

 of pigment in an eye is a secondary one, as we learn from 

 the sight of albino varieties. What precisely the significance 

 of pigment may be in relation to the cells in which the optic 

 nerve ends, is not yet agreed upon by physiologists. 



Of Euscorpius Italicus, Kos. — In figs. 3 atid 4 two 

 sections are drawn of the lateral eye of the little Italian 

 scorpion, as seen after removal of pigment. They are more 

 highly magnified than the eyes drawn in figs. 1 and 2, being 

 in actual size considerably smaller than the corresponding 

 eye ofAndroctonus funestus, as shown by a comparison 

 of the measurements given in the explanation of the plate. 

 The hypodermis cells are relatively to the nerve- end cells 

 coarser than in Androctonus funestus. In all essential 

 respects the eyes of the two species agree. The marginal in- 

 different cells or perineural cells of the ommateum are larger 

 relatively than in A. funestus, and so are the interneural 

 cells, which are correspondingly less numerous than in A. 

 funestus. The rhabdom is larger and thicker in E. italicus, 

 whilst further the nerve-end cells present a special structure 

 which is not in any way indicated in the nerve-end cells of 

 A. funestus. Each nerve-end cell contains, besides its nucleus, 

 a globular, highly refringent body (figs. 2, 3, k), quite uncon- 

 nected with the rhabdom, though of a substance similar to 

 that of the rhabdom. These bodies, which it is convenient 

 to term " phaospheres," are usually to be found below the 

 nucleus of the nerve-end cells, that is to say, near the fila- 

 mentary extremity of those cells. But there are some nerve- 

 end cells in every lateral eye of E. italicus which have the 

 phaosphere placed in front of the nucleus (fig. 4, /). This 



