Tlie Structure of Diatoms. By Dr. J. H. L. FUgel. 675 



at the mid-rib, fig. 45, so tbcat at the side of it are two thin 

 membrane- striae free from dots, sucb as we demonstrated in the 

 surface-image. This fine line I consider to be the hmit of the 

 inward projecting transverse striae, and also of the one touched 

 by the section ; for if it is thicker and comprises two transverse 

 striae, it will be looked for in vain in this image, because the 

 interference at the margin then becomes so strong that we can give to 

 the line any interpretation we please. The central nodules and their 

 expansion are not met with with certainty in either series ; unfor^ 

 tunately they seem to have broken off at the touch of the knife. 



The girdle-band in old valves has always a distinct row of coarse 

 striae ; in the surface-section, fig, 40, this is magnificently brought 

 out. These striae are about half as fine as the transverse striae of 

 the ventral valve. In the younger part of an old valve, or in a 

 young valve, the striae on the girdle-band are very indistinct. In 

 the transverse sections, inasmuch as the sections are in the direction 

 of these striae, nothing can be seen ; one observes no differentiation 

 whatever in this membrane except that sometimes irregularly a dot 

 appears on the inner side, which may indicate the delicate lines 

 running parallel to the marginal lines. The whole matter is to me 

 doubtful. I cannot explain the extremely fine structureless section 

 occurring at the margin of the surface section 1. Since the girdle- 

 band has no such non-striated portions in the surface view, it may 

 possibly be an outer substance hardened by the alcohol. 



The serial sections which were made in a direction 90° from 

 the preceding (22 in number) cut through the surface from first 

 to last ; but shortly after the first and shortly before the last, as a 

 glance at fig. 33 discloses, the transverse lines of the strongly 

 porous valves must, at the point where the two sides run parallel, 

 have been struck exactly vertical to their direction. This, as a 

 matter of course, occurs likewise with several valves situated between 

 the two ends. Further, the girdle-band is seen in several sections, 

 and is cut vertically to its striae. The most suitable sections 

 through the part of the dorsal valve under examination, as repre- 

 sented in fig. 48, show that the transverse lines, as we learnt from 

 the surface view owe their origin to the dehcate but distinctly 

 raised thickening lines on the inner side of the membrane. These 

 fine lines are about • 9 //, high, the membrane itself is • 5 /a thick. 

 In examining the sections near to the last one, one detects the 

 fact not quite so distinctly in those which are unquestionably 

 taken through the ventral valve, but I have obtained with a well- 

 regulated position of one section an unequivocal image, fig. 47. 

 Between the transverse striae lies the chamber, seen only with very 

 fine sections, fig. 50. As a matter of course, the valve-section is 

 in places entirely surrounded by the adjoining girdle-band section. 

 The girdle-bund can always be easily distinguished in these sections 



