NOTE. 



By an oversight, the references to pages in the Annotations, p. 496 el seq., 

 are erroneous, not having been altered to adjust them to the difference of 

 the paging in this volume and the original essay. The following corrections 

 must be made: 4 = 346; 7 = 348; 8 = 349; 9 = 350; 10 = 351; 

 12=353; 13 = 354; 16 = 357; 20 = 360; 23 = 363; 25 = 364; 

 90 = 421; 106 = 445. 



In reference to the discussion on the subject of measurement at p. 418, 

 it may be worthy of attention that Kiitziug confesses that Ehrenberg's 

 figures, drawn with an amplification of 300, are not smaller, but sometimes 

 even larger than his own, which are magnified 420 times. (Note on 

 Epithemia ocellaia, ' Kieselschal. Bacillarien,' p. 34.) 



