HISTORY OF DIATOMS. 



17 



valves, exactly oversteps a divisional period (generation) ; ind in this way the 

 duration of division is retarded. 



As a result of what has preceded, the following law can be formulated : 



"The largest daughter cell divides during the (N + i) th consecutive 

 divisional period ; the smallest daughter cell, on the other hand, first 

 divides during the (N + 2) th period exactly." 



This law not only requires that there should be a considerable delay 



in multiplication by division, but it also arrests the constant diminution of the 



cells in a marked manner ; it follows from this that the diminution in size 



is not carried on simultaneously with the multiplication by division, and that 



this diminution is only produced in a limited degree. 



For as far as the birth of Auxospores can be attributed to the diminution 

 of the size of the frustules, so can the rarity of their production be 

 explained by the phenomenon just described. 



The effect of the law is comprehensive ; if, for example, the diminution 

 of size after forty-three divisions in the cells of Melosira arenaria is such 

 that the production of auxospores becomes necessary, as must be admitted 

 in the face of known facts, then it follows from the law enunciated 

 that a single auxospore will be produced in the present case ; while on 

 the other hand, if the division is effected according to the generally 

 received rule, and as enunciated above by Mr. Deby, 1,052,100,000,000 

 auxospores ought to have been brought into existence. 



The general application of Otto Muller's law can scarcely ever be verified 

 in solitary species, and it can only be verified in filamentous species 

 when the smallest daughter cells of twin groups are morphologically 

 distinguishable from the larger daughter cells, as is the case with the Melosira 

 we have been considering. 



In every case each species will probably follow its own peculiar law, which 

 we shall probably never know, because the conditions under which they have 

 to be studied are so unfavourable. For this reason then an exhaustive 

 knowledge of the facts which prevent the too rapid diminution of size in 

 any given species is of special importance, and Otto Muller has rendered 

 a signal service to science in discovering and elucidating phenomena, the 

 existence of which had not even been suspected. 



One of the principal originators of Bacteriological Science, Dr. P. 

 Miquel, Director of the Microscopical Department of the City of Paris 

 (Montsouris Observatory), has lately turned his attention to Diatoms. 



Dr. Miquel has introduced into the study of these Alga? the same methods 

 of cultivation which he has employed with such marked success in the study 



c 



