The Rev. W. Smith on the Diatomaceae. 3 



mence at a single parent cell, and go on by successive self-divi- 

 sion of the cells formed from it. The invariable occm-rence of 

 this mode of growth in a tribe so extensive as the Diatomacece 

 and embracing forms so varied, is surely a presumptive proof 

 that these organisms belong rather to the vegetable than the 

 animal kingdom. 



The process of fissiparous or self-division in the Diatomacece 

 is far more frequently to be seen than that of conjugation, and 

 may indeed be detected on almost every occasion that these 

 forms present themselves to our notice. Besides its bearing 

 upon the question above alluded to, a clear understanding of this 

 process is important as making us in some degree acquainted 

 with the internal structure of the Diatomaceous frustule, and 

 supplying an easy mode of distinguishing its diflfei-ent portions 

 and aspects. I shall therefore give a concise description of the 

 process of self-division, as it has appeared to me to take place in 

 every instance which has fallen under my notice. This descrip- 

 tion will in some respects differ from that given by other ob- 

 servers, and involve views of the structure of these organisms not 

 hitherto maintained ; it is therefore right that I should state that 

 its authority rests solely on personal observation. 



A Diatomaceous frustule consists of a cell, the membrane of 

 whose wall possesses the vital power of secreting an external coat- 

 ing of silex ; this silex being deposited in two plates or valves, of 

 varied form in the different species, and decorated with the most 

 beautiful and diversified sculpturing, produced by the arrange- 

 ment and relative position of series of lines, dots, depressions, 

 furrows or ribs. 



In stating that the siliceous valves are deposited exterior to 

 a cell-membrane, I am at variance with the opinion held by most 

 wiiters upon the subject, the general idea being, that the silex of 

 the Diatomacece exists in intimate union with the membrane of 

 the cell, whose wall is believed to consist of " cellulose penetrated 

 with silica." Such is the view advocated by Meneghini in his 

 treatise ' Sulla Animalita della Diatomee,' p. 20, a translation of 

 which has been kindly furnished to me by Chr. Johnson, Esq., 

 of Lancaster. In the same passage Meneghini alludes to the 

 views of Nageli, who, he alleges, contends that the silex is depo- 

 sited exterior to an organic membrane. I have no means of 

 ascertaining on what grounds Nageli rests his opinion, which 

 seems to coincide with the view I have adopted ; but I am able 

 to supply one important fact in its support, having in my pos- 

 session numerous specimens of a Stauroneis (probably the S. as- 

 pera, Kiitz.), in which the valves, after a slight maceration of the 

 frustules in acid, have in part or wholly become detached from 

 the cell -membrane, leaving a scar on its walls bearing the distinct 



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