TfiE DESMIDIACE.E. 97 



easily be mistaken for a single animal. But the microscope, 

 the great revealer of hidden wonders, shows it to be of a 

 far different and far 

 more complicated na- 

 ture, as no less than 

 two or three thousand 

 minute green spots or 

 cells, often connected 

 by green threads, and 

 each enjoying its in- 

 dividual life, are here 

 united to a hollow 

 sphere. From each of 

 the spots proceed two 

 long cilia, so that the 

 entire surface is be- 

 set with these vibratile 



Volvox Globator (much, magnified). 



filaments, to whose 



combined action its movements are due. Within the external 

 sphere there may generally be seen from two to twenty other 

 globes of darker colour, and of varying sizes. The smaller of 

 these are attached to the inner surface of the investing sphere, 

 and project from its cavity ; but the larger lie freely within, and 

 may often be observed to revolve by the agency of their own 

 ciliary filaments. After a time the original sphere, too narrow 

 to contain its growing progeny, is rent asunder, and the con- 

 tained spherules, swimming forth and speedily developing 

 themselves into the likeness of that within which they have 

 been formed, in their turn give birth to new colonies, the 

 parents of future generations. 



Such is the wonderful history of the Volvox, whose countless 

 numbers frequently cover the surface of stagnant ponds and 

 ditches to the depth of several feet, in multitudes so dense that 

 the single spheres are hardly separated from each other by in- 

 tervals of three or four times their own diameter. 



Another highly interesting form of minute vegetable life is 

 that of the Desmidiacece, simple cells generally independent of 

 each other, but sometimes joined together in linear series by 

 means of a gelatinous exsudation. The outer coat, which fre- 

 quently possesses an almost horny consistence, but does not 



ii 



