942 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Its broken surface was peculiarly adapted to bring out tbe valuable 

 qualities of the vertical illuminator. I first focused on tbe lower 

 lamina, where the upper was entirely removed from it. This was not 

 quite in contact with the cover-glass, and consequently could not be 

 seen so easily as it otherwise would have been. The refraction of 

 the light made it appear black (as a very thin transparent film on a 

 black background), but the hexagonal outlines where the hexagonal 

 walls were broken away, and the central circular areolas were still to 

 be seen with careful looking. I then turned to the thicker part of 

 the shell, and here came an unlooked-for surprise. I immediately saw 

 that there were two classes of appearances to be examined. 1st. In 

 small patches over the surface from which the upper lamina had 

 been removed the hexagonal walls stood up here and there like islands. 

 These walls were evidently thickened and incrusted with a white 

 substance apparently more porous than the silex, and this incrustation 

 took the form of nodules at the angles of the hexagons, whilst it 

 partly filled the hexagonal cell at the bottom, giving it a hemi- 

 spherical or cup-like form. 2nd. Beyond the general line marking 

 the fracture and removal of the upper lamina, and where it was still 

 in place, the surface was smooth and in all respects of the same 

 appearance as the lower surface seen on the first specimen. This I 

 repeated and re-examined till I felt sure of my observations, and that 

 there was no illusion about it. Three classes of appearances stood 

 there as opaque objects, too clear for question : 1st, the black, lower 

 lamina with faint hexagonal and circular markings ; 2nd, the island- 

 like portions of the hexagonal cells without the upper film, and 

 incrusted with the white substance; and 3rd, the upper lamina 

 surface, smooth and grey, with its darker hexagonal tracing and 

 circles within. 



But it occurred to me to add another test. Whilst the surface 

 was still illuminated by the vertical illuminator I threw a beam of 

 light through the achromatic condenser from the mirror below, and 

 now had what seemed demonstrative evidence, making assurance 

 doubly sure. The lower film was plainly seen, very thin, with shallow 

 circular areolation, the hexagonal lines being almost invisible ; the 

 patches of cell-structure stood out vividly, less changed than the rest ; 

 but the unbroken part of the structure with both laminae in place, 

 made transparent by the strong, transmitted, bluish light (the con- 

 denser had a blue moderator), showed the internal structure exactly 

 as in the island patches, whilst the fainter red beam of light from the 

 vertical illuminator still marked the gleam of the upper surface by 

 reflection, and the whole structure stood revealed. By turning on 

 and off the transmitted light from the mirror the surface view or the 

 internal structure could be seen in turn, and the fascinating experi- 

 ment was repeated again and again." 



As to MM. Prinz and Van Ermengem's statement that the centre 

 of the " eye-spot," viewed by transmitted light, never shows any film, 

 it is true that along a broken margin of a separated inner lamina of 

 Coscinodiscus the eye-spot is usually found empty ; but this, Dr. Cox 

 says, is not always so, and in the unbroken portions of such a plate 



