lfi DERM i |>- OF THE IMTI'h - I \ I I R. 



The cell, that is t<> say, the plant, is multiform, varying from the 

 simple cylindrical and fusiform, to the denticulate, crenulate, lobed 

 and otherwise much indented margins of the equal part.- into which 

 the cell is with few exceptions, beautifully and symmetrically 

 divided. The division <>f the cell into two equal part- is effected 

 by a transverse constriction, usually so deep as t< leave aboul a 



third of the diameter of the < stricted > 1 1 for a connecting link 



between the two parts; - stimes, however, the constriction is so 



slight as to produce merely an obtuse angled sinus sach side of 



the cell ; a few have no constriction. 



The wall {cytioderm) of the cells is not constituted alike for all 



the genera; in some cases it appears to I f a siliceous character, 



judging by the appearance of the empty case, and by the firmness 

 with which it retains the contour of the cell, even years after the 

 desmid has been collected ; bul usually the wall is more fragile and 

 easily liable to collapse or rupture, unless the specimen is kept in a 

 preservative fluid. 



One of the characteristics of Desmids which confirmed many of 

 the earlier microscopists in the belief of their animal character, was 



their seemingly voluntary movements. These vements are most 



apparent in the larger forms of Closterium and Cbamorttm, but 

 are more or less evident in all of them; thej consist of slow, steady 

 oscillations, and sometimes the} go forward and backward, similar 

 t" the movement of diatomes, l>nt slower, therefore less observable. 

 By mean- of this locomotive power, they work themselves t the 

 surface when gathered int<> a vessel with dirt and other foreign 

 matter, and colled in such positions as are most exposed to the 

 light. Many theories have been advanced to account for this 

 phenomenon, but hitherto all have failed to establish a satisfactory 

 explanation. 



Another movement belonging to the Desmids is that of the 

 granules within the cells. This is always present in good living 

 specimens, and i sists in a circulation of granules in the watery 



* 



fluid next the eel] walls; they appear to be constantly passing to 

 and fro between the centre and the end- of the cells. 



A third motion belongs to the so-called vacuoles of Closlerums, 

 Docidiums and Peniums. In the end of many of these celle is a 

 well-defined globular, transparent space (vocuole) filled with a 

 number of small granules, significantly called, by the Germans, 

 tanzenden komchen, or dancing granules, because of their sprightly 



