HARDWICKE'S SCIENCE-GOSSIP. 



123 



the underlying calcite leaves an impression easily 

 recognisable, which does not correspond with the 

 convexities or concavities of the inferior surface. 



The thinned transverse sections, when the thickness 

 is less than half that of an alveole, also clearly prove the 

 existence of openings in the inferior layer ; the mem- 

 brane that closes the bottom of the alveolae is mani- 

 festly broken (interrompuc) at its centre, and this 

 lacuna is included on each side between the turgid 

 parts (est comprise de cheque cote cntre des parties 

 renflees), where the section is more or less crescent- 

 like. 



The sections of Trinacria also demonstrate the ex- 

 istence of pores traversing the entire thickness of the 

 siliceous envelope. 



The aspect which presents the junction of the 

 double connection of Coscinodiscus in a longitudinal 

 section (coup normal) indicates that their growth 

 takes place at the free margins (Wallich), and not by 

 intussusception or the addition of a third internal 

 connective (Cox). The naissant valves are formed of 

 a single layer of silex and perforated ; they develop 

 centrifugally (O. Miiller). In some preparations the 

 valves of Trinacria are covered with a membrane, 

 opaque and black in colour, and which shows 

 similar perforations. This is probably the last layer 

 of the cellular envelope, feebly silicified or entirely 

 organic, reduced to a state of carbon by the slow 

 combustion of its cellulose. The existence of this 

 layer is admitted by many authors (Dippel) ; and 

 chemical analysis also proves that this black matter 

 is carbon. In the interior of the frustules is seen the 

 spheroids, sometimes completely filled. In a normal 

 section of Coscinodiscus it has been ascertained that 

 the perforated tips of the dots on the inferior siliceous 

 layer of the valve penetrate and force their way into 

 the hexagonal cavities of the alveolar layer. 



Among the mineralised diatoms found in the 

 London Clay, and in which the silica has been re- 

 placed molecule for molecule by iron pyrites, these 

 perforations are also present (Kitton). Certain Cos- 

 cinodisci approaching very nearly to those found in 

 the rock from Fur, frequently show by cleavage the 

 inferior layer and its perforations on the place in 

 which it had been imbedded. The sections of this 

 clay which the authors of this memoir have prepared 

 demonstrate this very clearly. 



A discussion, in which many of the members took 

 part, followed the reading of the paper. 



M. Delogne said that the principal conclusions of the 

 writers of this memoir were not opposed to some ideas 

 he had formed of the structure of certain species. He, 

 however, did not wholly believe that, in consequence 

 of the existence of the perforations in the siliceous 

 carapace, the plasma came in direct contact with 

 the water in which the diatom lived. An internal 

 membrane which closes the pores may probably exist. 

 The presence of these perforations was not opposed 

 to the vegetable nature of the diatom cell, and he 



did not think that they should be allied to the 

 Polycystina, as some had done. 



M. Barre informed the meeting that in some re- 

 searches on the Guano diatoms he had noticed certain 

 facts which absolutely confirmed the presence of the 

 perforations, as stated by MM. PrinzandVan Ermen- 

 gem in the test of Coscinodiscus. 



In reply to M. Delogne, M. Van Ermengem said 

 that there could be no doubt that the Diatomacere 

 belonged to the vegetable kingdom. He must 

 nevertheless observe that Borscow and Pfitzer had not 

 been able to obtain the reaction characteristic of 

 cellulose n the membrane of the envelope, and that 

 their morphological type was far apart from that of 

 CEdogonium, Desmidise, and Schizochlamys, to which 

 some had compared them ; but it was even more 

 difficult to find analogies between them and the 

 Polycystina, animals to which they most nearly 

 approached. Owing to these considerations, they 

 had been ranged by Hackel in his kingdom Protista, 

 where they formed a separate class. 



F. Kitton, Hon. F.R.M.S., 

 Cor. 7ii e j jib. d. I. Soc. Beige d. Mic. 



NOTES ON THE SCHIZOMYCETES. 



{Continued from page S6.] 



Appendix. 



~\ T 7ITH the Schizomycetes we may range several 

 V V other genera which are partly united with 

 them by others without remark, but which present so 

 great peculiarities, that it will be better provisionally 

 to separate them. 



XIV. SphtEROTILUS, Kiitzing. Cells roundish- 

 angular or oblong, rounded at the corners, united in 

 great numbers in a colourless gelatinous sheath to 

 form long threads, which are densely tufted and en- 

 tangled in floating flakes. Multiplication by means 

 of vegetative cells, which isolate themselves and then 

 form new threads by continued subdivision. Repro- 

 duction by spores, which are produced endogenously 

 within the vegetative cells. 



68. S. nutans, Kiitz. 



Flakes in the vegetative stage yellow-brown in the 

 older parts, colourless in the younger, many times 

 branched, very slimy. During spore formation, partly 

 milk-white, partly red-coloured. Cells 4-9 /j. long, 

 3 (x thick. 



In stagnant and flowing water. 



The flakes consist of an enormous mass of long, variously- 

 combined threads, which are formed of rows of cells, surrounded 

 by a slimy, evanescent sheath. These threads often assume a 

 shrubby branched form, and are attached to water-plants, or 

 float in a thin layer on the water. In the formation of spores, the 

 protoplasm of the cells breaks up into numerous, minute, strongly 

 refringent portions, which become round spores, red at maturity, 

 afterwards of a brown colour. These are set free by the dissolu- 

 tion of the mother cell. They germinate very quickly, and grow 

 into threads which are either isolated, or united with the parent 

 threads or with other threads as well. These daughter threads 



G 2 



