1853.] Linnean Society. 267 



bodies under high magnifying powers is such, that even with 

 lenses most carefully corrected and fully sufficient for all general 

 purposes of investigation, we are left altogether in doubt as to 

 whether or not the phaenomena of colour arise from refraction. 

 He uses lenses made by Ross about eight years since, a quarter 

 and an eighth of an inch, the latter of excellent defining power, 

 and is convinced that these are not inferior to any glasses in use on 

 the continent. But with them, particularly the latter, delicate 

 membranes seen edgeways exhibit a blue tint, under certain cir- 

 cumstances, often giving rise to a difficulty in arriving at a decided 

 opinion in questions connected with cellulose, when using the 

 sulphuric acid and iodine test. Many phaenomena might be cited in 

 reference to this subject, but the main point to which he wishes to 

 direct attention is, the doubt existing in his mind as to the nature 

 of the red spot described by Ehrenberg as an ' eye ' in the Infusoria. 

 He has observed this object chiefly in the unicellular Alg(e and 

 zoospores, and was first led to suspect that the red colour depended 

 on unequal refraction, in the cells of Chlamydoinonas Pulvisculus. In 

 these he has frequently found several red spots on one individual 

 cell, which however could not all be brought into focus at once, and 

 he has decidedly observed, that when these spots were brought into 

 clear and well-defined focus, they appeared as bright colourless 

 granules. Frequently no red spot at all could be found. 



The idea suggested by this was further confirmed by noticing 

 the similar variations of colour according to form in a granule 

 (nucleolus ?), in a half- decomposed, colourless, diseased cell. 



Finally, he had recently found that he could bring out the crimson 

 colour most beautifully in the central spot or ' hUum ' of starch 

 granules. When the lens is a little too far away from the object, 

 the hilum appears like a minute black spot ; then, carrying the lens a 

 little nearer, it comes out as a beautiful crimson spot exactly like an 

 ' eye- spot ' in every respect. Adjusting the focus exactly, by bringing 

 down the lens a little more, the hilum is seen as a well-defined spot 

 of a brighter character than the rest of the starch-grain, but altogether 

 devoid of any prismatic colour. 



Although dwelling but briefly on this question here, Mr. Henfrey 

 states that he has had it under consideration for some time, and he 

 thinks it desirable to make known his supposition now, in order that 

 other microscopists working with diff"erent lenses may direct their 

 attention to the point, and furnish the results obtained with them, 

 since almost all high objectives differ slightly in their correction. 



