90 UEV. E. o'^IEARA. 



plate joasscs freely across the cell, reaching from one row of 

 Ifccl-piincta to the other. When the friistule so stands as 

 that the keels are to the eye of the observer super-imposed 

 one on the other, a narrow dark brown longitudinal band 

 appears between two broad colourless ones. If, again, the 

 frustule lies on one obtuse-angled edge, it appears entirely 

 light yellow-brown. And again, if the frustule or one 

 girdle-band lie parallel to the slip on which the object lies, 

 the colouring of the cell, which would naturally be white, is 

 of a somewhat darker hue, because the endochrome-plate 

 will be projected in a direction inclined to the plane of its 

 acute-angled side. 



We have consequently among the Nitzchiece species with 

 the inner and outer structure symmetrically diagonal, some 

 having the silicious envelope and the soft inner parts unsym- 

 metrical to one another on the homologous sides ; and lastly, 

 intermediate forms in which the silicious envelope is dia- 

 gonal, and the inner structure unsymmetrical to it on the 

 homologous sides. The cell-division has been followed out 

 in Nitzschia elongata and iV. sigmoidea. It commences with 

 a longitudinal division of the endochrome-plate from the 

 ends throiighout, then the nucleus separates into two, 

 and the division of the plasm ensues. The daughter-cells at 

 first lie in the longitudinal axis of the cell, and then after, a 

 time assume their natural position. 



Ceratoneis, Ehr. 

 The minute forms, C. acicularis (Kiitz.), Pritch., and C 

 reversa (W. Sm.), Pritch., as regards their inner structure 

 differ in no respect from the normal Nitzschiem, with a single 

 endochrome-plate lying on one girdle-band ; but on the 

 contrary, C. longissima (Brib.), Pritch., exhibits numerous 

 minute plates. 



Bacillaria. 



The single cells of Bacillaria paradoxa, Gmel., have like- 

 wise a single endochrome-plate covering one girdle-band ; 

 nevertheless in the greater number of the cells of a colony 

 the endochrome-plate appears separated into two through 

 means of division. As respects the development of auxo- 

 spores in the Nitzscldea>, we know only this, that Schuman 

 found a form belonging to Nitzschia with zone-covers 

 (zonenkleide) . In addition to the coarse dark zones, there 

 was present also a system of fine longitudinal lines on the 

 sheath. 



It is to be regretted that Dr. Pfitzer should have given 

 the authority of his justly-distinguished name to the revival 



