HISTORY OF DIATOMS. 



2. Movement of Diatoms. A large 



number of diatoms, especially those which have a 

 naviculoid form, are endowed with the power of 

 locomotion, the cause of which is not yet ascer- 

 tained, and which has exercised the imagination 

 ot a large number of observers. 



Of the numberless hypotheses which have been 

 put forward to explain the motion of diatoms, that 

 which has been advanced most frequently is the 

 supposition of the existence of cilia ; this is also the 

 suggestion of Mr. Jacob D. Cox, of Cincinnati, 

 one of the most learned diatomists of our 

 age, in a small work ( J ) recently published by 

 him. Mr. J. D. Cox believes that the raphe is 

 the seat of a line of cilia, which act in the 

 groove formed by the raphe, and which Prof. 

 H. L. Smith declares to be a genuine cleft. The 

 narrow line of epidermis at this spot being covered 

 with active cilia, one can easily understand, 

 says Mr. Cox, that the formation of silica on 

 this line would be obstructed or hindered. Still 

 more recently Mr. O. Biitschli, ( 2 ) Professor of Zoology at Heidelberg 

 University, has revived the idea of a cilium or very fine flagellum, and 

 thinks that by means of it the phenomenon under consideration can 

 be explained. Unfortunately, up to the present no staining re-agent 

 whatever has been discovered which will throw these filaments into 

 relief so that their existence has never been demonstrated. 



Professor H. L. Smith has for a Ions; time studied the motion of 

 diatoms with great care. We cite below a passage from a letter, in which 

 this scientist describes some interesting phenomena which he was able to 

 observe during the movement of certain diatoms. 



" If a living Finnularia is followed under the microscope after the field 

 has been coloured blue by indigo, and when the valve side is in view, 

 that is to say, with the median line turned towards the eye, small particles 

 of indigo will be observed to move along the whole length of the 

 median line, and then to accumulate near the centre in the form of a 

 small ball or sphere. 



Fig. 4. 

 Navicula viriais. 



A. Valve or valve face. 



B. Girdle or zonal face. 



(') Diatoms, their nutrition and locomotion, by Jacob D. Cox, in The Microscope, July, 1890. 

 ( 2 ) Mittheilung iiber die Bewegung der Diatomeen. Heidelberg, 1892. 



