TERATOLOGY OF DIATOMS. 



*3 



It thus happens that on certain diatoms very singular filamentous 

 parasites are occasionally found, which are thought to be algae. The 

 Nitzschia especially are frequently attacked in this way, and in the Atlas 

 to my Synopsis (pi. 7, fig. 22) will be found a representation of a 

 Nitzschia a?ignstata infested in this way. 



Recently Mr. Grenfell (') has noticed various disciform diatoms having 

 radiant filamentous appendices, which are very long, excessively thin, and 

 fairly numerous. Every specimen of his gathering was in this condition 

 (fig. 21). I have also personally established the existence of similar 

 radiant appendices on the Coscinodiscus excentricus from a gathering 

 made at Sheerness-on-Sea. 



Fig. 2i. Diatoms with filamentous appendices. 



The important question in all these cases is whether the appendices 

 are true parasites or whether they are actually produced by the 

 frustule ; it is to be hoped that this problem will be solved by sub- 

 sequent research. It is advisable in every case to draw attention to 

 these appendices, as they are only to be seen with difficulty, and can 

 only be seen to advantage when the living frustules are placed upon a 

 slide and there allowed to dry of their own accord, the drop of liquid not 

 being covered over with a cover-glass. 



It would be well to try the effect of analine stains on gatherings in a 

 living state to see whether these productions are not more frequent than 

 is at present believed. 



(') On the occurrence of pseudopodia in the Diatomaceous genera Melosira and Cyclotella, 

 by J. G. Grenfell, Q.J.M.S., 1891. 



