PEOCEEDINGS OF SOCIETIES. 255 



September 28th. — Microscopical Meeting. The President, Mr. 

 W. M. Hollis, in the chair. Subject " Diatoms." 



Mr. Wonfor, who introduced the subject for the evening, said he 

 approached it with some dif&dence in the presence of some, especially 

 of Mr. Hennah, who had devoted much time to the study of diatoms, 

 and who knew much more about them than he did. 



Diatoms were unicellular algfe of a peculiar character, distinguished 

 from other unicellular plants, and especially the desmid, to which 

 they bore a great resemblance, by the possession of a silicious covering 

 which, while it rendered them exceedingly brittle — hence their name 

 brittle worts — also made them all but indestructible imder ordinary 

 circumstances. One great j)eculiarity with them was the fact that if 

 the internal cell membrane became exposed to water, it secreted a sili- 

 cious covering, and if the plates forming the frustule became separated 

 a plate of silex began to form, and became what was termed the con- 

 necting membrane. 



The frustules were either free, i. e. moved freely in the element in 

 which they were found, from which circumstance they had been called 

 animals ; adherent or attached to the substances on which they grew, or 

 aggregated ; in this last case they cohered either by their angles, were 

 provided with a gelatinous pedicel, which united the frustules together ; 

 or they were enclosed in great numbers in a general thallus. 



The separate frustules as seen from a front or side view presented 

 veiy different appearances ; in fact, some like the coscinoclisci were 

 circular in a front and nearly rectangular in a side view, with a line 

 down the centre, which showed the junction of the two frustules. The 

 cell contents of the frustule were a viscid protoplasm called the en- 

 doclirome, generally of a brown or yellowish colour, containing globular 

 and gi'anular bodies, of which the latter had been seen in some cases 

 to rotate within the cell, so forming a species of cell-circulation. 



The mode of increase was by self-division and by conjugation ; in 

 the former, the valves separated, the cell contents aggregated on oj)- 

 posite sides of the frustules, the primordial utricle folded in, became 

 contracted, and eventually separated, at the same time a new silicious 

 valve was secreted by each half, and the result was two diatoms in the 

 place of one. This mode of growth was very rapid. In multiplica- 

 tion by conjugation, two frustules lying near each other oj)ened at 

 their sutm'cs and exuded theii" cell contents, which coalesced, while 

 the whole was involved in a gelatinous substance, from which sprung 

 a frustyle of larger size than the parents, to which the name sporan- 

 gial frustule was given. 



The silicious valves had, from their markings, always been 

 favoui-ites with microscopists, and though some complained of too 

 much time being devoted to diatoms, yet the question of the nature of 

 their markings had been the means of improving objectives, and had 

 also led to the designing various forms of illuminating apparatus more 

 or less simple or complicated. 



A discussion ensued, in which the President, Messrs. Home, 

 Robertson, Wonfor, Glaisyer, and Hennah took part, the last-named 

 gentleman drawing especial attention to the researches of Dr. Maddox, 



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