The Structure of Diatoms. By Dr. J. H. L. Flogel. 691 



chambers erroneously suggest an outer opening. In the left valve these vertical 

 chamber-vralls appear on the inner side serrated (naturally, with both, the inner 

 surface is on the left) ; this also is an optical delusion. In both valves the very 

 dark walls are much thicker and more clearly expressed than in a reliable image; 

 but the lumen of the chambers is reduced and strongly rounded off (also wrong !). 

 The connection between the vertical walls with outer and inner membrane 

 appears therefore like a thick nodule ; whilst with good sections little can be 

 traced of such end thickenings. 



3. Pinnularia major. Extremely thin longitudinal section exactly through 

 the chamber-openings, focus and magniticatioii as in 1. This is probably the 

 best section in my collection, and can be recommended for all finer measure- 

 ments. The best focus is from a to 6; less good from b to c. Tlie section 

 direction runs in the line 1, photograph 1. One sees (best with the help of a 

 lens) the club-like thickening of the chamber-walls; one can measure the 

 thickness of the outer membrane, &c. The inner surface is on the right, proved 

 by the bend in the section. On the left is a surface section of another valve. 



4. Finnularia major. Collodion impression of the outer surface of a valve, 

 in air. Produced by Schroder's dry 1/6, x 298. The strongly black mar- 

 ginal line is the expression of an elevation in the collodion originating in 

 the same maimer as we shall see when we come to photograph 5. The mid- 

 rib is distinctly seen ; it is a delicate ridge, corresponding to the cleft in the 

 valve, and ends at the central nodule with a stronger point. The smooth space 

 on both sides of the mid-rib slopes, beginning at that portion of the surface 

 where the chambers are situated in the valve, and is there slightly difierent ; 

 this ditierence probably originates by a change in the evaporation processes. 

 Starting from the upper corner on the right we observe on the cast a chain of 

 numerous small crystals of unknown origin (on the preparation itself). The lines 

 on the left are Newton's rings in the thin collodion film. All other dotting 

 is the granulation of the collodion surface. 



5. Finnularia major. Collodion impression of the inner surface of a valve. 

 Produced as No. 4, same magnification. With regard to the general sketch of 

 the valve the following is to be observed : — If in making a collodion cast of a 

 valve (shown in fig. 119 as s) lying with its surface towards the slide (v), the fluid 



Fio. 119. 



naturally fills up at first all the inner spaces. In hardening th.e mass contracts, 

 and occupies afterwards as a solid film the shaded space c in the image. The 

 quantity that originally entered into the angle between valve and glass thins 

 away and appears as projection v ; this accounts for the remarkable enlargement 

 of the outline in the cast in comparison with that of the valve. Next to the so- 

 foimed dark surrounding edge follows an inner portion partly lighter, partly 

 darker, and often interrupted. Tliis is the depressed furrow in which lay the 

 extreme edge of the valve {vide photograpli G), and had been so squeezed into 

 the collodion that during the separation from the valve many small fragments 

 of this 8culi)turele88 edge remained behind in the furrow. On the surface 

 one observes the impression of the central nndule, and further two longitudinal 

 lines. These represent the collodion which ran into the chambers (i:ida text), 

 and are mised ribs (A o in the fig). In several places are seen the threads 

 described in the text. A part of this longitudinal line is drawn in fig. 7; 

 conf. their description. (Tliese niis'd ribs I have sometimes seen on casts 

 of extremely small undefined I'innularia ; one would otherwise only look for them 

 in Navif.-ul'x. Tlie real details can only be learnt from largo varieties.) On 

 the left of th(! cist a large air-bubble had been enclosed in the collodion ; 

 near its centre we observe the granulation, elsewhere so distinct, decrease, which 

 circumstance I have made use of for the explanation of the faint granulation 



