ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
235 
valvis dissimilibus, una tantum lineam et nodulum 
medianum liabens (Cocconeideae, Achnantheae). 
/?. Frustula symmotrica, valvis similibus (Gomphonemeae, 
Cymbelleae, Naviculeae). 
Series II. Frustula latere aucta, axi infravalvari longitudinalem 
aequante vel saepius exsuperaute, cingulo plerumque 
lato et patente sculptura preedito. 
a. Cingulo simplice baud tesselato (Hemiaulideae, Bid- 
dulphieae). 
/?. Frustula cingulo late extenso, partibus pluribus prae- 
textis composito (Striatelleae, Rhizosolenieae). 
Nutrition and Movements of Diatoms.* — Dr. J. D. Cox adopts Van 
Heurck’s view of the alveolation of the siliceous coat of diatoms, and 
believes that it is by endosmose through the alveolae that they 
receive their nutriment. On the other hand he considers that the chief 
locomotive organ of diatoms is the raphe, when present, and that the 
habit of the species depends on the presence or absence, and on the 
position and form, of this organ. Thus, for example, the symmetrical 
Naviculae are furnished with a well-developed raphe along the median 
line of each valve ; Cocconeis, with its raphe situated on one side only 
of its large and flat disc, is adapted to an epiphytic life on the stems of 
other Algae ; the curved species of Surirella have no proper movement, 
except a slight rolling from time to time ; their raphe is found on the 
border of the wings. Other Pseudo-raphideae or Cryptoraphideae are 
carried without resistance by waves and currents, or vegetate quietly in 
a bed of mucus, following a mode of existence in accord with the 
conditions by which they are surrounded. 
/3. Schizomycetes. 
Prof. R. Koch on Bacteriological Research.! —In an address on 
bacteriological research, Prof. R. Koch gives a rapid sketch of the history 
of Bacteriology, the age of which is computed to be about fifteen years. 
After acknowledging that our present knowledge is in great measure due 
to, and in fact has been rendered possible by, the great improvements 
in Microscope objectives and in the methods of technique (prepara- 
tion, preservation, cultivation, &c.), the author lays it down as being 
incontrovertible that all species of bacteria are constant, but admits that 
within certain limits they may deviate from the normal type, the patho- 
genic being most prone to variability. The confusion which has 
frequently arisen with regard to the species of bacteria is ascribed to the 
undue prominence given by some writers to certain characteristics, and it 
is held by the author that the proper method of determining the specific 
position of micro-organisms is to very carefully consider every charac- 
teristic, morphological and biological. And even when this has been 
done there are numerous difficulties to be overcome ; for example, to 
isolate and identify the typhoid bacillus from the contents of the intestine, 
from the soil or water, is difficult evon for the experienced observer. 
* Journ. de Micrographie, xiv. (1890) pp. 207-12, 245-7. 
f ‘ Vortrag gehalten in der 1. allgemeinen Sitzung des X. Internat. Med. Con- 
gresses 1890,’ Berlin, Hirschwald, 1890, 8vo, 15 pp. 
