Movements 



103 



surrounding medium which originated in the outer cleft of the anterior half 

 of the raphe, such a current carrying with it a small quantity of mucus 

 secreted by the exposed protoplasm. Whatever mucus may be secreted in 

 such a thread, the amount is much too small to cause the movements of 

 a diatom as large as Navicula major. O. Miiller has also carefully studied 

 these threads and states that the movements of the diatoms which form 

 them cannot be caused by the backward thrust of such a thread. 



Fig. 75. Navicula ( Pinnularia) major Kiitz. 1, individual cell immersed in Indian ink ; 2 and 

 3, valve and girdle views respectively, showing the narrow threads to which are attached the 

 particles of ink. (From Oltmanns, after Lauterborn.) 



A band-like thread of much larger size has been described and figured 

 by Schroder ('02) as being formed by Amphipleura pellucida. This is a 

 sluggish diatom with scarcely appreciable changes of position, and the 

 secretion of such a mucous band might be sufficient to account for the feeble 

 movements which occur. 



The movements of diatoms are not all of a uniform character, and it is 



