838 



SUMMAEY OF CURRENT RESEARCHES RELATING TO 



constantly observed what appeared to be gelatinous casts of diatoms. 

 In order not to lose these, I Lave been content to select diatoms from 

 what would be called dirty strewed mixed slides. 



In the beginning of 1878, when watching diatoms in their living 

 state, I observed what I thought was a Cocconeis moving freely, and 



there appeared to be an undu- 

 Fig. 147. lating movement along the 



edge all round. On trying to 

 isolate it I lost it under the 

 cover. 



In December 1878 I came 

 across what appeared to be a 

 cast of a diatom (Stauroneis 

 pulchella), of which I send 

 two photographs * by direct 

 and oblique light. The 

 latter is for the purpose of 

 showing the plasticity of the 

 material more distinctly. It 

 is represented by Fig. 147. 

 The striae on three-fourths of 

 the figure may be seen to be 

 perfectly distinct and separate 

 along the median line ; they 

 then generally coalesce or 

 intertwine, separating again 

 on nearing the edge of the 

 membrane. In the remaining 

 quarter the striae have ap- 

 parently coalesced completely, 

 and have formed with the 

 membrane a continuous sur- 

 face to the point, and beyond. 

 If this be a cast, it strongly 

 suggests movement by cilia or 

 undulating membrane. 



It may be said that this is 

 simply an imperfectly siliceous 

 frustule. It must be remem- 

 bered, however, that the diatom in question had to go through the 

 usual operations of washing, &c. Also why is only one-fourth acted 

 upon up to the median line, whereas in the other three-fourths the 

 finest hair-like (or feather-like) portions are seen distinct at or near 

 the median line, but converging and intertwining towards the delicate 

 membranous looking edge ? 



I have also sent two photographs of a Pinnularia and cast, 

 by direct light, the one showing what I take to be the siliceous 

 frustule, well defined; the other the so-called cast, well defined, 



* The photographs are deposited in the Library. 



