174 The Shell of the Cuttle Fish. 



THE SHELL OF THE CUTTLE FISH. 



It is not generally known that the internal shell of the cuttle 

 fish (Sepia officinalis), so commonly found by the sea-shore, and 

 likewise having its place among the miscellaneous items of the 

 chemist's shop, affords one of the most beautiful objects for 

 microscopic examination by polarized light. All that is re- 

 quired is to scrape a little of the soft part of the shell with a 

 penknife, taking care not to reduce it to too fine a powder, 

 and then mount it in Canada balsam. The slide is thus easily 

 prepared, but to view it requires some little nicety. If ex- 

 hibited without a selenite stage, the polarizer and analyzer 

 should be so adjusted as transmit their least amount of light. 

 When they are in this position the cuttle shell slide may be 

 placed on the stage, and there will be seen a number of irregular 

 shaped masses of a dull golden hue, variegated with numerous 

 points of a brighter aspect, and likewise many more or less 

 oblong fragments, glowing with rich purples, crimsons, yellows, 

 emerald-greens, and shades of golden-brown. The colours or 

 tints are arranged in numerous horizontal bands which, under 

 an inch or two-third object-glass, show symptoms of crystal- 

 lization in the shape of thousands of minute needles, an aspect 

 that is strengthened if a higher power, such as a quarter or a 

 fifth, is employed. Revolving the analyzing prism produces no 

 good effects, nor does a similar process with the polarizer, the 

 object presenting no beauty except in the one position we have 

 described. While the prisms are in such relative positions as 

 to transmit little or no light, the selenite stage may be intro- 

 duced beneath the slide, and the colours will appear somewhat 

 more brilliant, but pretty much the same. Revolving the 

 analyzer still exhibits only one good view, namely, that with 

 the dark ground, on which the fragments glisten like jewels 

 upon black velvet. But if the polarizer is made to take a 

 quarter turn, and the selenite is of the right thickness, a revolu- 

 tion of the analyzer will then exhibit two new effects, one 

 exhibiting brilliant colours on a rich sky-blue ground, and the 

 other on a ground of an amber tint. The blue one is exceed- 

 ingly fine. A thin slice of mica, about the thickness of writing 

 paper, placed under the slide and on the selenite, affords further 

 changes of extreme richness and beauty, the grounds assuming, 

 as the analyzer revolves, crimson, violet, and green hues, with 

 corresponding alterations in the colours of the particles of the 

 shell. 



If the experimenter is successful in adjusting the prisms, 

 and employing the right thickness of selinite or mica, this object 

 is quite equal in splendour to the most esteemed crystals, such as 



