276 FIRST FORMS OF VEGETATION. 
drained off. But not only does the whole Desmid 
move itself in the water in this way, its cell-con- 
tents also exhibit various movements similar to 
those of Chara, Vallisneria, and Anacharis. Large 
globular granules flow in uninterrupted currents 
on the inner surface of the utricle. The course of 
the currents is not very determinate, and they seem 
to pass each other in close proximity, continuing 
however for hours moving in the same manner. 
By using the fine adjustment, a single granule may 
often be followed in its course round the end of 
the cell, down the edge and across the suture, thus 
affording a beautiful demonstration of the unicel- 
lular character of the plant. Like many other 
fresh-water alge, the Desmids are ordinarily repro- 
duced in two ways, by simple cell-division, when 
each frustule divides into two; and by the conjuga- 
tion of the two cells of a single filament, or of two 
separate filaments, producing by their organic 
union and the blending of their endochrome, a 
spore whose granular contents become gradually 
brown and red, while their coats become thickened, 
granular, or even spinous, resembling bodies found 
fossil in flint, supposed to be the spores of Des- 
mids. 
But before concluding this chapter I must refer 
to an organism which has for a long time been 
considered by all authors to be an animal, but is 
