124 On the Examination of 



Into the question of the affinities of the llotifers I do not intend 

 to plunge. I shall consult my own tastes and capacities better by 

 hunting for a four-leggal rotifer, now that I have found a six-legged 

 one. At some future time I hope to return to the examination of 

 Pedahon's structure. Its length is about Ti>(jth of an inch from the 

 front of the trochal disk to the extremities of two curious cihutod 

 projections at the posterior end of its body. 



II, — On the Examination of Mixed Colouring Matters tvifh the 

 Spectrum Microscope. By H. C. Sorby, F.E.S., &c. 



In studying the colouring matters soluble in water that may be 

 obtained from various kinds of Algse, for which special names have 

 been proposed, as though they were single and simple substances, I 

 have been led to conclude that they are in some cases mixtures of at 

 least four, which are readily distinguished by their spectra. The 

 facts which have thus presented themselves have so impressed me 

 with their importance in such inquiries, that I think it may be well 

 to make the study of mixed colouring matters the subject of a 

 special communication. The interest of this question, in connection 

 with certain branches of botany, will, I trust, be made fully apparent 

 when I have shown that various kinds of marine and fresh-water 

 Alffie, and even some Lichens, though differing very much in general 

 tint, may contain one or more particular colouring matter in com- 

 mon, and differ in the presence or absence of others. There is thus 

 a bond of union between somewhat remote members of certain 

 natural orders, whereas without proper attention each of these 

 mixed colours might be thought to be a special kind, and no such 

 connection between the plants would be recognized. 



The manner in which the mixed nature of some colouring matters 

 may be ascertained from their spectra has been already described 

 by Professor Stokes* and others, as well as in previous papers by 

 myself; but in order to make this communication complete in itself, 

 I must be allowed to again describe some of them. I shall not 

 attempt to enter into the chemical part of the subject, or to treat of 

 the separation of different substances by purely chemical methods, 

 such as the solubility or insolubility in various reagents, but con- 

 fine myself almost entirely to those processes in which the exami- 

 nation of the spectra is of primary importance. I scarcely need say 

 that the coloured material should be separated, as far as can be con- 

 veniently managed, into that which is soluble or insoluble in such 

 simple solvents as water or alcohol ; but at the same time there are 

 cases in which such a difference in solubility does not appear sufficient 



* ' Journal of tlip Chemical Society,' .June 2, 18(>4 (New Scr.), ii., pp. :J04-v51S, 



