278 ANDREWS. [Vol. V. 



in toto for twenty-four hours or on the slide for about two hours, 

 all that was made out in macerations regarding the structure of 

 the refracting cells may be seen again in sections, as also the 

 relative arrangement of these cells and the smaller pigment 

 cells. Thus transverse sections, such as Fig. 11, show the tran- 

 sition of the ordinary epithelium into that forming the eye, the 

 peripheral position of nuclei of small pigment cells, the more 

 central position of the larger nuclei of the refracting cells, as 

 well as the structure of these latter identical with that seen in 

 isolated cells. 



The inclusions have often a clearer, very highly refracting 

 central part, that may be exposed by a section cutting one side 

 tangentially, as in one case in the above figure. In many prep- 

 arations, both sections and surface views, this central or interior 

 part of the inclusion contains a number of minute drops or 

 vacuole-like spherules seen in Fig. 12. The basal end of these 

 refracting cells, their cup-like part separated in macerations, is 

 clear and somewhat vacuolated in sections, as if having a watery 

 consistency readily acted upon by shrinkage, etc., in the process 

 of preparation. The axial part between the nucleus and inclu- 

 sion is sometimes made of alternating areas, as in macerations ; 

 more often, however, granular, and even entirely clear, so that 

 one is led to suppose this region easily changed by different 

 reagents. 



The cell outlines are faintly marked, in various methods of 

 staining, and show the necessarily radiating arrangement of the 

 cells in fitting into the hemispherical eye mass. The marked 

 difference in shape, diameter, and position of the nuclei of the 

 two sorts of cells is especially noticeable ; many sections show 

 those of the refracting cells arranged very uniformly in a circu- 

 lar arc, while those of the simple pigment cells have no constant 

 distance from the cuticular surface of the eye. 



The cuticle over the eye is very thin and delicate, as else- 

 where, and neither in sections nor in any other mode of prep- 

 aration could any apertures in it be seen corresponding to the 

 projections of the inclusions, yet such may exist. 



In tangential sections the same appearances are met with as 

 in preparations having pigment, except that the nuclei are much 

 clearer and their positions more definitely determinable. As 

 seen in a section (Fig. 12) near the surface of the eye, the nuclei 



