690 Transactions of the Society. 



Fig. 46. — The dorsal valve of a cell with the cell-nucleus from the second 

 transverse section series. 



Fig. 47 X 660. — Longitudinal section through a ventral valve in the direction 

 of line 4, fig. 33. 



Fig. 48 X 660. — Longitudinal section through a dorsal valve in the direction 

 of line 5, fig. 33. 



Fig. 49 X 660. — Section quite through the girdle-band in the direction of 

 line 6, &t^. 33. 



Fig. 50. — A portion of fig. 47, 



„ 51.- „ „ 48, 



„ 52.— „ „ 49, 



highly magnified, g, the ridge-sl.aped tranoverse lines projecting inwards, p, tl.e 



fine dots between them (? chambers). 



Fig. 53. — Synedra Gallionii, 

 Any middle transverse section through a frustule. 



EXPLANATION OF THE PHOTOGRAPHS DEPOSITED IN THE 



LIBRAEY. 



All photographs except No. 12 have bc-en made by me personally without 

 eye-piece according to the old method with wet plates. No touching up has 

 been done to any of them. No faults in the negatives are specially mentioned, 

 but they can easily be distinguished from the objects used in demonstration. 



1. Pinnularia major ; large specimen in balsam ; a little more than half a 

 valve. Produced by Schroder's immersion 1/18 in. ; x 631. 



The lines on the tracing paper covering the photographs which can be con- 

 nected by a ruler, indicate the direction of the sections iu the space between 

 a and 6 : — 



1 is the direction of the longitudinal section fig 5, pliotograph 3. 



2 „ „ 6, and portion of photograph 2. 



3 „ transverse section 4. 



1 ,. ,, 1. 



5 „ „ 2. 



6 „ oblique section, photograph 7. 



7 „ transverse section of the valve m in photograph 6. 



On the right-hand side the chamber openings are distinctly seen ; in making 

 liuemr the median edges of tliese edges are t lUched ; in tiie same manner Ir 

 will touch the lateral edges. On the left and in other places on the valve the 

 focus is nut so good, although both edges glimmer everywhere. 



From c to c/ is the region where presumably the mid-rib shows the depresbion 

 almost at right angles on the transverse section (fig. 3). From c to the end- 

 uodule e, and from d to the line 7, the mid-rib is simply a vertical incision (fig. 1). 

 /, irregularly formed chambers on the right ; the walls are here black and vanish 

 at the lateral end. 



2. Pinnularia major. A coarser longitudinal section through two valves lying 

 one in the other. Like all other following sections, so here the section is im- 

 bedded in gum, the entire gum-chip surrounded by balsam. Position and 

 mignification as in 1. The focus from a to 6 is the best; one sees in the valve 

 on the right the transverse sections of the chambers with the inner membiane 

 which closes the chambers ; the section direction is approximately the same as 

 with line 2, photograph 1. In the valve on the left the openings are seen, but in 

 consequence of the gieat thickness of the section the oblique ridge-shaped 

 vertical chamber-walls glimmer and disturb the image, and which only becomes 

 quite intelligible by photographs 3 and 7. In the lower part is a zigzag-ahaped 

 cleft r through the gum-chip ; there the section is very thick and the focus 

 unsuitable. This will convince us what errors can arise with a coarse object 

 through mistakes in focus and cutting, and which in a less degree occur with finer 

 objects like I'leurosigma. The valve on the right has lost the outer membrane, 

 which has apparently btuck on the gum on the right ; the vertical chamber-walls 

 are therefore torn off L,t the point of connection with this outer wall, and the 



