The Struciure of Diatoms. By Dr. J. H. L. FUgel. 679 



the accuracy of these views which I acquired in the examination of 

 the sections, I should have been obliged to photograph an entire 

 series. 



The question whether the diatoms become smaller through 

 repeated division can be well elucidated with Achnanthes, espe- 

 cially if one is possessed of richer material than I have, and by 

 examining and comparing the measurements. In doing this we 

 should start with the marginal lines of very young specimens. 

 What I have seen in my examination of Achnanthes preparations 

 confirms the results obtained by Braun and others, especially 

 Pfitzer (19, pp. 20-3, 100-102) with Eimantidium. I confess I 

 see several specimens in which the younger valve is shorter than 

 the older ; but I have also found some where the length is greater 

 than in the older, which may possibly be caused by the girdle-band 

 having enlarged itself at the edge. The normal condition appears 

 to me to be an exact equality of both valve-lengths. On the one 

 hand this follows from the manner above described in which the 

 first traces of the young marginal line are developed, fig. 34, and 

 where with the best methods of measurement no difierence will be 

 found. On the other hand one sees, by careful examination of such 

 young cells, that the older girdle-band is always shghtly raised, 

 that is to say, about as much as its thickness ■ 4-0 ■ 5 /* ; to this 

 extent it grows over the old valve. Next, one can often see with 

 Achnanthes longer cell-rows in connection, all of equal size. This 

 has been minutely discussed by Pfitzer. We have lastly in 

 Achnanthes in so far a very favourable object, that the valves are 

 not similar as with Pinnularia and Himantidium, but on the 

 contrary are very different, and no definite judgment can be arrived 

 at with regard to age and number of generation. Now, if I 

 examine a few good rows composed of eight frustules, where for 

 example the lowest and oldest ventral valve is together with the 

 youngest dorsal valve coming out of the third division, then I fiod 

 no difference in size between the grandfather and the great-grand- 

 daughter, although the threefold thickness of the girdle-band, 

 always a good measurable size, would have to be deducted with 

 the latter if Pfitzer s theory were in this instance correct. How- 

 ever, who will guarantee that we have here to do with the grandfather 

 and the great-granddaughter ? The hundredth division may already 

 have taken place, since it is known that in time only individuals 

 connected by mucus are thrown off. All considered, I am of opinion 

 that Achnanthes contradicts rather than confirms Pfitzer 's theory, 

 and that the supposed corrective of the cell diminution, namely, 

 the formation of auxospores, may have other purposes. The decision 

 of this question must bo left to future investigators. Whether tlio 

 corner of the ventral valve developing the longer or shorter spine 

 by which this diatom ia fastonccl on other algao, is of different 



