200 = Structural and Physiological Botany, 
to occur in Didymium Serpula, where arate of 10 millimetres 
in a minute has been observed. | 
The antherozoids and swarmspores (zoospores) of many 
Cryptogams were long considered to belong to the animal 
kingdom ; and they actually show so close a resemblance to 
animals that they might well have been described as plants 
in the moment of their transformation into animals. The 
swarmspores of Alge are particles of protoplasm which break 
through the walls of the cells in which they are formed, and | 
swim about for a time in water like animals. It is only 
since it has been ascertained that they give birth, after a 
shorter or longer period of rest, to a plant of the same species 
as that from which they sprang, that their vegetable nature has 
been absolutely determined. ‘The internal forces by which 
these swarmspores (Fig. 385, p. 252), and the antherozoids 
(Fig. 371) which are endowed with motion of a similar nature, 
Fic. 371.—Antherozoids : I. of Nitella syncarpa (Characez. x 500); II. of 
Gdogonium gemelliparum (Algz. x 800). 
are enabled to perform their movements, are still unknown ; 
but they are certainly connected with the vibratile cilia, or 
minute threads of protoplasm of different lengths and vari- 
able number, the vibrations of which set the body in 
motion. But it must be admitted to be a most wonderful 
contrivance for the maintenance and propagation of a 
number of vegetable organisms. 
Neither swarmspores nor antherozoids are provided with — 
a cell-wall—or, at all events, with only an extremely delicate 
one— during their period of motility. Still more remarkable 
than these must, therefore, be considered the movements of 
the Diatomacee, | Desmidieze], Oscillatorieze, Spirulineze, and - 
some other organisms which are enclosed in a complete cell- 
