538 



NATURAL SCIENCE. 



each shell valve, little clumps of fine granules of Indian ink were 

 formed, which increased gradually by the addition of more 

 granules. After a time it could often be observed that a fine thread 

 shot out from the heap of granules, which ran along the raphe, though 

 not directly upon it, to one end of the diatom. 



The investigation of a specimen lying upon the zonal side gave 

 a clearer insight into the real course of the phenomenon (see Figure). 

 From in front of the diatom a stream (a) of loose granules, each 

 separately suspended in the liquid, flows along each side in a back- 

 ward direction towards the nodal point of the raphe [k). At this spot 



/ 



Optical section of a Pinnularia nobilis in movement, in zonal view, n. Nucleus; c, the Centro- 

 so'iie ; v, the peculiar double threads in the protoplasm ; a. the granules flowing back to the nodal 

 point (k) of the anterior raphe ; 6, the jelly thread shooting out backwards, which has rolled itself up 

 into a tangle on the right side. The arrows show the direction of the movement of the Diatom, the 

 granules, and the thread. 



All the details drawn in the figure can be plainly observed in the living Diatom. 



they become fastened together by an invisible connecting medium, 

 and then continue to travel backwards united into a thread [b), which 

 passes obliquely outwards and backwards, becoming thus further and 

 further removed from the surface of the shell-valves. As the thread 

 is formed the diatom moves forward in the direction of the arrow. 

 It is evident that here we have to do with a thread which is simply 

 made visible by the sticking together of numerous Indian ink 

 granules. This can be recognised (i) by the regular arrangement of 

 the granules in rows, (2) by the cessation of the usually so lively 



