HISTORY OF DIATOMS. 1 3 



quently they are displaced the whole length of the perimeter of the 

 protoplasmic current, which is enveloped in a glaireous bed so as finally to 

 come together in front of the anterior opening of the central nodule. There 

 they collect together so as to form a filament by the plasm, which is stopped 

 from time to time, and this filament is drawn out by the plasm as it continues 

 to ooze out. 



The smaller Pinnularia and other Navicula show no signs either of a 

 glair or filament. Nevertheless, their movement acts in the same way as in 

 the case of the three species enumerated above. And even their anatomical 

 structure, the system of canaliculi and fissures, as well as the arrangement of 

 the currents which are observed in them, are in all respects identical. 



Consequently one is forced to conclude that the emission of the 

 gelatinous matter is the motive agent. Midler's theory of the mechanical 

 causes of their motion explains the displacement of these smaller species in 

 the same manner as that of the larger, with this unique and subsidiary 

 difference only, that the plasm of the larger species generally secretes during 

 its movement a glaireous matter, which is not the case with the smaller species. 



3. Multiplication and Reproduction of Diatoms. Diatoms multiply 

 by self-division and are reproduced by conjugation. 



When multiplying by self-division the nucleus commences by splitting up, 

 and the division of the internal membrane takes place at exactly the same 

 period that this phenomenon does in the cells of higher plants ; the act of 



deduplication of the primordial utricle is 

 brought about with very great rapidity. 

 It commences to show itself at the 



Deduplication of the' primordial utricle of tW0 ends f the frUStule at the P intS 

 a Pinnularia (H. L. Smith). a an( j (fi g- 7 ) . t h e membrane there 



forms a fold which gradually lengthens so as to reach the nucleolated mass 

 in the centre about six minutes after the commencement of the phenomenon. 



According to Mr. Robert Lauterborn the division of the nucleus is always 

 caryokinetic. Dr. Miquel on his part has seen in some Nitzschia the single 

 primitive nucleus dividing into two coloured areas, each spread out like a fan, 

 together assuming the shape of a spindle. Consequently he admits that 

 phenomena of caryokinesis are possible in the case of diatoms. 



According to Dr. Miquel the division of this primordial utricle would not 

 be brought about in the way Professor H. L. Smith indicates, but that it only 

 commences when the nucleus is completely deduplicated, and when the 

 nuclei which are being formed are completely separated from one another. 



While this sub-division is proceeding the connecting zone is correspond- 

 ingly enlarged, and the internal membrane afterwards secretes a new silicious 



