122 Transactions of the Royal Microscopical Society. 



II. — Further Notes on Frustulia Saxonica. 



By W. J. HiCKiE, M.A., St. Jolin's College, Cambridge. 



{Head be/ore the Royal Microscopical Society, January 5, 1876.) 



Plate CXXX.* 



Before I make any remarks on Dr. Woodward's paper, I would ask 

 permission to read a letter whicli I have just received from Dr. L. 

 Eabenhorst, late of Dresden. His letter is as follows : 



"Villa Lttisa, by Meissen, December 27, 1875. 



"Honoured Sir, — In reply to your favour of the 11th of this 

 month, I must frankly acknowledge that I still fai-thfully remember 

 that you showed me one evening in Dresden, and therefore by 

 lamplight, Frustulia Saxonica, with its distinct and sharply out- 

 lined strise-system ; but I must also as faithfully and frankly ac- 

 knowledge that I subsequently, and only lately, failed myself to 

 resolve the longitudinal lines with one of Gundlach's strongest 

 immersion lenses.j But then I must observe that I work only by 

 daylight, and never by lamplight, out of regard for my eyesight. 



" If now Dr. Woodward maintains that Frustulia Saxonica is 

 identical with Navicula crassinervis, we must suppose that he is 

 ignorant of one or other of them. 



" Yours respectfully, 



" Dr. L. Eabenhorst." 



It will be observed here that Dr. Eabenhorst states that what 

 I showed him was Frustulia Saxonica, and that I showed him 

 both lines ; for his expression, " Streifensystem," includes both lines. 

 I will now hand over Herr Seibert's photographs for your 

 inspection, when I have first read his letter which accompanied 

 them. 



" Optisches Institut von Sexbert & KuAFFT, Wetzlar, 

 " December 20, 1875. 



" Honoured Sir, — I herewith send you the two photographs 



you wished for, and hope they will enable you to convince Dr. 



Woodward that the lines do exist. They can be seen only by the 



help of direct sunlight ; better, however, when the light is modified 



by some blue material. Of course, very good objectives are required 



for the purpose ; but it is not the strength of the objective that 



conditions the visibility. One can see them with my No. 7 ; 



better, however, with my No. 8, one of which you possess. To be 



sure, the stronger objectives show the striae more easily, but with 



DO real advantage. ^^ -tr . .n ^^ 



^ lours most respectfully, 



"W. Seibert." 



* Tins Pliite reprcsciit.s the two separate jihotogTaplis sent by Herr Seibert, aud 

 lal)rlled by him "Frustulia Sachs." The pliotoi^^raphs liave been enlarged twice 

 in the Plato. Only oue-half uf the striao of each frustule has been reproduced. 



t This is easily accounted for. Dr. Eabenhorst told me himself, that his 

 slides of Frustulia Saxonica were such poor things in comparison with the ones I 

 showed him, that he should not care to let me see them. 



