The Structure of Diatoms. By Dr. J. H. L. Flogel. 695 



space (a) ; here the outer entrance-opening is touched (6). Tlie section is only 

 thin enough and focused correctly at a. Below, near the marginal portion, 

 another piece of diatom lying by accident on the valve has been touched. 



18. Surirellt biscriafa. Collodion rast in air. Production and magnification 

 like photograph 4; it is the cast of the inner surface of a valve. The deep 

 black edge is a raised collodion ridge, wliich is f^irmed on the outer side of the 

 wing as described above with Pinnularia. The distinct border next to it is a deep 

 brown of the collodion; in it must have beeu the valve edge (figs. 13-17). The 

 dark ribs on the surface are raised places, i. e. wave-elevations, the clearer inner 

 spaces are de[)ression3. At the lateral end of each wave-elevation, not far from 

 the di.-tinct marginal line, is a dark dot. In the cast is a vertical projection ; 

 these thorn-like spines naturally are the contracted outlets of the channels. In 

 the mid-;ib a stria of the valve has remained behind. Collodion surface remark- 

 ably smootii. 



19 and20. /sMmiacneriis. Two successive sections. Production as in 1 ; x 633. 

 The one section must be adjusted to the other like a mirror image. The separate 

 sections are A, B, C. The i-ituation of the cells in the gum has unfortunately not 

 been figured before cutting, and it is now almost impossible to define them ; but 

 80 much is certain, a few sections further on A and B coalesce, consequently both 

 belong to one cell, whilst C is a second cell, apparently touched nearly trans- 

 versely. B is therefore, as its small extent teaches, doubtless a section through 

 the extended end of the rhomboidal cell, either through a free corner or more 

 probably through the isthmus proper. This is here important. 19 is a very thick, 

 20 is a very thin, section in which the isthmus section is a little injured ; the 

 section of the cell C is flapped over at the top or pushed together. In both 

 sections one sees in the ring B on the inner side ridge-projections, which are the 

 Cause of the well-defined cell-marking. Had I given this with only one section, 

 some severe critic might have retorted that the ridges might be on the outer side, 

 and that the apparent inner projections were obliquely struck in projecting 

 marginal portions. Such like opposition is refuted by the image of the second 

 section. Designating here the projections, for example, 1, 2, 3, &c., one will find 

 that all fit exactly one to another except that, instead of No. 3, photograph 20, 

 we see two projections standing close together in photograph 19, evidently because 

 here in the first instance an areola corner was touched. This comparison proves 

 further, that the membrane was touched exactly vertically by the section on the 

 right side in photograph 19 (or on the left in photograph 20), but on the opposite 

 side obliquely. The more reliable thinner section 20 proves undoubtedly the 

 tuming-in of the ridges and the outer smoothness of the membrane. 



The section through the cell C is by far too thick for the study of the 

 sculpture. In section A are found a few places in photograph 19 (just below the 

 middle), where it has the required thinness for the observation of the very thin 

 ridges on the outer side of the membrane. Judg ng from the numerous examples 

 of these images in other sections I can only declare it to be the girdle-band. 



BIBLIOGRAPHY. 



1. Abbe, Prof. E. — Beitrage zur Theorie des Mikroskops und der mikrosko- 



pischen Wahmehmung. Arch. f. Mikr. Anatomic, ix. pp. 413-68. 



2. Deby, F. — Note sur I'argile des Polders suivie d'une liste de fossiles qui y ont 



ete' observes dans la Flandre occidentale. Annales de la Socie'te' Malaco- 

 logique de Belgique, xi. 1876. 



3. DiPPEL, Prof. L. — Beitrage zur Kenntniss der in den Soolwassern von Kreuz- 



nach lebenden Diatomeen, sowie iiber Structur, Theilung, Wachsthum 

 und Bewegung der Diatomeen uberhuupt. Kreuznach, 1870. 



4. Engelmann, Prof. Th. W. — Neue Methode zur Untersuchung der Sauer- 



stfjfTausscheidung pflanzlicher und thieriacher Organismen. Botanische 

 Zeitung, 1881, pp. 441 et seq. 



5. Flogel. — Ueber optiache Erecheinungen an Diatomeen. Bot. Zeitung, 1869, 



pp. 713, 729, 753. 



