DIATOMACEJE ; PHJiOSPOKE.E 625 



ments which have recently been introduced in the construction and 

 mode of using the sub-stage condenser require to be put into prac- 

 tice. But to those who have the time, the will, and the appliances, 

 there is a fine field now open for working, to a far higher point than 

 we have touched at present, the true structure of such diatoms ,-is 

 can be made amenable to the powers possessed by our best recent 

 optical appliances ; and for the leisure of a professional or commercial 

 man we know of no more suitable and attractive employment for the 

 microscope. It will often be convenient to mount certain particular 

 forms of Diatomacece separately from the general aggregate ; but, on 

 account of their minuteness, they cannot be selected and removed 

 by the usual means. The larger forms, which maybe readily distin- 

 guished under a simple microscope, may be taken up by a earners- 

 hair pencil which has been so trimmed as to leave two or three hairs 

 projecting beyond the rest. But the smaller can only be dealt with 

 by a single fine bristle or stout sable-hair, which may be inserted 

 into the cleft end of a slender wooden handle ; and if the bristle or 

 hair should be split at its extremity in a brush-like manner it will 

 be particularly useful. (Such split hairs may always be found in a 

 shaving-brush which has been for some time in use ; those should be 

 selected which have their split portions so closely in contact that 

 they appear single until touched at their ends.) When the split 

 extremity of such a hair touches the glass slide, its pails separate 

 from each other to an amount proportionate to the pressure : and, on 

 being brought up to the object, first pushed to the edge of the fluid 

 on the slide, may generally be made to seize it. A very experienced 

 American diatomist, Professor Hamilton (Smith, strongly recom- 

 mends a thread of glass drawn out to capillary fineness and flexi- 

 bility, by which (he says) the most delicate diatom may be safely 

 taken up, and deposited upon a slide damped by the breath. For 

 the selection and transference of diatoms under the compound 

 microscope, recourse may be had to some of the forms of ' mechanical 

 linger' which have been devised by American diatomists. 1 



Phseosporeae. The greater number of the seaweeds exhibit a. 

 higher type of organisation than any that has hitherto been, described. 

 The old classification of seaweeds into Melaiaosporece, Rhodosporece, 

 and Chlorosporece, according as their colouring matter is olive-brown, 

 red. or green, cannot altogether be retained. Under the head of 

 fhoeosporecB are now included a very large number of the brown and 

 olive-brown seaweeds. In ascending this series we shall have to 

 notice a gradual differentiation of organs, those set apart for repro- 

 duction being in the first place separated from those appropriated 



1 For a description of those of Prof. Hamilton Smith and Dr. Rezner, see Journ. 

 of Roy. Microsc. Soc. vol. ii. 1879, p. 951, and that of Mr. Veecler, vol. iii. 1880, 

 p. 700, of the same Journal. 



[A very large number of observations have-been made during recent years by 

 Castracane, O. Miiller, Lauterborn, Comber, Murray, Miquel, and others, on the 

 structure of the diatom-valve, on the various modes of reproduction, and on the 

 phenomena accompanying their apparently spontaneous powers of motion, and 

 several schemes of classification of the genera have been proposed. On these, too 

 numerous to mention here, and some of which still require confirmation, the reader 

 should consult the successive volumes of the Journal of the Royal Microscopical 

 Society. ED.] 



S S 



