180 DESCRIPTION OF [Poly(/asirica. 



along the whole length of the plant. The function of 

 these bodies is very difficult to determine ; but they are 

 to be found in very many conferva, and are perhaps to be 

 likened to the spermatic animalcules of plants. 



"Under the great family BacillariaEhrenberg has brought 

 thirty-five to thirty-six genera ; but which may be more 

 properly divided into two separate families — the family of 

 the true Bacillaria, and that of the Desmidiacea. This last 

 family has already been firmly settled by Menegheni, and 

 includes those true Algae upon whose nature there can be 

 no doubt. To the true Algae belong the following genera 

 of Ehrenberg's Bacillaria : — Desmidium, Ag. ; Stauras- 

 trum, Mey. ; Pentasterias, Ehr. ; Sphaerastrum, Mey. ; 

 Xanthidium, Ehr. ; Scenedesmus, Mey. ; Odontella, Ag. ; 

 Pediastrum, Mey. (Micrasterias, Ag.) ; and Euastrum, 

 Ehr. In all these genera, nothing has yet been observed 

 which can be adduced as evidences of their animal nature. 

 Actual motion, arising from internal causes, I saw only in 

 Sphaerastrum ; and the slight movement, supposed to 

 have been observed in some of the genera, is certainly of 

 the same description as that of some conferva, which 

 sometimes vegetate far below, at other times upon, the 

 surface of water; but this elevation from the deep is 

 generally connected with visible evolution of gaseous 

 matter. The increase by self-division occurs in all these 

 genera ; this process is looked upon by Ehrenberg as one 

 of the strongest and most decisive characters of animal 

 nature ; but I have elsewhere proved, in the most satis- 

 factory manner, that self-division is very common, l)oth 

 in the lowest plants as well as in the elementary organs 

 of the more highly developed ones. The little vesicles 



