SPECIES IN THE DIATOMACEiE. 135 



alike in allied species of the simpler forms, such as Cocconema, 

 Cymhella and Navicula, that our determination must be in- 

 fluenced by less important considerations, and the habitat, 

 outline, and arrangement of the cell-contents, all require to be 

 brought under review before we should feel justified in con- 

 stituting a species. 



It may be said that, to describe and figure every variety 

 that presents itself to our notice, will aid future observers in 

 the study and determination of these forms. If practicable, 

 this course might be a desirable one ; but this is no more 

 possible in Diatoms than the representation of every leaf, 

 which varies however slightly in form and size from anotlier, 

 would be possible in our description of a forest-tree ; and the 

 elevating of such diversities into specific distinctions, and the 

 conferring a distinct name upon each aberrant individual, seems 

 to me a course more likely to confuse and to embarrass than 

 to lead to a clear arrangement or satisfactory system. Besides, 

 it overloads a scientific arrangement with a cumbrous nomen- 

 clature, which unduly taxes the time and patience of future 

 observers to simplify or remove. 



It is, therefore, far better to expend our labour in endea- 

 vouring to combine, unite and harmonize the interminable 

 varieties of nature, and thus in a few brief and simple 

 terms to embrace a number of seemingly different, but truly 

 identical, specific forms, than to encumber science with a 

 phraseology which alarms the general inquirer, and enhances 

 the labour of the more studious observer. 



