Life-histori/ of some Marine Diatoms. By J. D. Siddall. 381 



mounting in sea-water, formalin, and a trace of osmic, seems to 

 promise much in this dii'ection, but the difficulties in the May 

 at present seem almost insuperable. 



The occurrence of pseudopodia in Diatomacese has, I know, 

 been suggested, debated, and dismissed as undemonstrable many 

 years ago. In this connexion I have permission from Mr. Mainland, 

 of Tenby, to copy a portion of a letter from him to Mr. Waddington. 

 He says: — " I well remember Mr, J. C. Grenfell bringing the 

 matter before the Quekett some twenty years ago, but I can only 

 find the record of his exhibiting at the Conversational Meeting, 

 June 5, 1891. He noticed the phenomenon in Cyclotella and 

 Melosira ; the general impression then was that the appendices 

 were parasites." I find, however, that Van Heurck, in his treatise 

 on the Diatomaceae, refers to Mr. Grenfell's paper on the subject in 

 Q.J. M.S., 1901, and says : — " I have also personally established the 

 existence of similar radiant appendices in Coscinodiscus excentricus, 

 from a gathering made at Sheerness-on-Sea. The important 

 question in all these cases is whether the appendices are true para- 

 sites or whether they are produced by the frustule. It is to be 

 hoped that this problem will be solved hy subsequent research. . . . 

 These appendices can only be seen to advantage when the living 

 frustules are placed upon a slide, and there allowed to dry of their 

 own accord, without a cover-glass It would be well to try anilin 

 stains on living examples, to see whether these productions are not 

 more frequent than at present believed." 



By the use of modern black-ground appliances in the investiga- 

 tion of these nettings, so kindly sent to me at very frequent in- 

 tervals all through the past winter by Messrs. Shepheard and 

 "Waddington, I have been able to demonstrate the presence of 

 pseudopodia in the two diatoms, without leaving room for doubt. 

 I have shown them to many good microscopists here, -and Mr. 

 E. M. Nelson has, I believe, also seen them. It seems to me quite 

 probable that Mr. Grenfell and Yan Heurck both saw them on the 

 same species, but the apparatus I have used was not then available. 

 I venture to hope that otlier observers more competent than myself, 

 by reason of a better acquaintance with Diatomacese and greater 

 technical skill, will be induced by these notes and observations to 

 take up the study of living DiatomacCce, with a view to the better 

 understanding of the meaning and purpose of the exquisite minutise 

 of theii- siliceous skeletons. 



