APPENDIX II 

 THE EYE-PIGMENT OF APUS 



IT was very difficult to decide whether the cells marked 

 / in the diagram (Fig. 43) of the eye of Apus were really 

 cells, as there drawn, or only collections of very minute 

 pigment cells. [Grenacher, in his drawings of the single 

 eyes of Apus, leaves the matter rather indefinite. He 

 indicates rather than draws the pigment cells with nuclei. 

 His drawing leaves the impression that he took it for 

 granted that they were large pigment cells, without actually 

 ascertaining the facts.] We were at first inclined to take 

 the latter view, having found that under a very high power, l 

 the granules themselves were not easy to distinguish from 

 cells. Each one consists of a stainable nucleus surrounded 

 by a pigment crust, the whole being enclosed in a layer 

 of some hyaline substance. These " cells J> were of all 

 sizes (from 1-2 //,), and were found in all stages of fission 

 (see Fig. 65). There are thus two ways of regarding 

 these pigment masses in the eye of Apus. Either the 

 whole is a kind of loose syncytium of minute pigment 

 cells, as we at first thought, or these pigment gran- 

 ules are formed inside a large cell around stainable 

 protoplasmic granules, as starch is formed round the 

 leucoplasts. This we now think to be the case. 



1 Zeiss apochromatic 2 mm. homogeneous immersion, 1.40 n.a., 

 eye-piece No. 12, giving 1500 diam. 



