102 



Bacillarieas 



there is a current passing along the outer cleft of the raphe from the 



anterior polar cleft to the anterior pore of the 

 central nodule, and a corresponding current in the 

 opposite direction in the inner cleft of the raphe. 

 Similarly, in the posterior half of the diatom there 

 is a current flowing from the posterior pore of the 

 central nodule along the outer cleft of the raphe 

 to the posterior polar cleft, and a corresponding 

 current in the opposite direction in the inner cleft. 

 These protoplasmic streams are connected by the 

 joining canal of the central nodule (fig. 65 2 sclil), 

 and it should be remembered that the cytoplasm 

 in the inner cleft of the raphe is really part of the 

 lining layer of protoplasm of the cell. 



Continued investigations by O. Miiller, from 

 1896 to 1909, on the structure of the raphe in 

 many of the larger diatoms, and on their move- 

 ments, indicate that in those forms with a high 

 development of the raphe the locomotion is due 

 primarily to the protoplasmic currents which are 

 circulating along this complicated cleft. It has 

 been shown that the pressure within the cell is 

 often as much as four or five atmospheres, and 

 therefore there is probably sufficient friction 

 between these circulating streams and the sur- 

 rounding water to bring about the movements of 

 the cells. 



The observations of Palmer ('10) on Surirella 

 elegans are certainly confirmatory of Miiller's 

 investigations. Palmer has shown that it is the 

 actual protoplasm which circulates along the raphe- 

 clefts in the keels of Surirella, and that the 

 protoplasmic streams reacting upon the sur- 

 rounding medium result in those peculiar rolling 

 and turning movements which are so well exhibited in this genus. 



Lauterborn has described and figured the formation of slender mucous 

 threads by Navicula major, which can be best seen when the diatom is 

 immersed in Indian ink. The thread apparently issues from the anterior 

 pore of the central nodule of each valve, extending in a direction opposite 

 to that in which the diatom is moving (fig. 75 3 and J). The mucous 

 threads are only discernible owing to the particles of ink, and it is not 

 improbable that they merely indicate the direction of a slow current in the 



Fig. 74. Girdle view of a large 

 Navicula. a, anterior open- 

 ing of canal in central nodule; 



b, posterior opening of same; 



c, polar cleft in the front 

 terminal nodule; d, opening 

 in posterior terminal nodule ; 

 e, anterior plasma-stream in 

 outer cleft of raphe; /, 

 posterior plasma-stream; g, 

 stream of granules when 

 Indian ink is added to 

 the water ; h, slender mu- 

 cous thread with granules 

 attached. The arrow indi- 

 cates the direction of move- 

 ment of the diatom. (After 

 0. Miiller.) 



