SECT. II. 



DESMIDIACE&. 191 



threads is immature and begins to expand into a hollow 

 sphere, then the central globe is continually bisected 

 so as to form 4, 8, 16, 32, 64, or a greater number of 

 equal and similar parts, each of which is ultimately de- 

 veloped into a zoospore exactly the same with the ma- 

 tured green zoospores on the surface of the primary 

 sphere, so that the ' Volvox globator is a composite 

 fabric made up of a repetition of organisms in all re- 

 spects similar to each other,' which Professor Ehrenberg 

 the first to discover, though he did not investigate the 

 development of the plant. 



It appears that certain spheres of the Yolvox are 

 monoecious, that is, each sphere contains male and 

 female cells, though the greater number of cells are 

 neutral. The germ or female cells are larger and of a 

 deeper green than the others ; the male cells resemble 

 them, but the endochrome within them breaks up symr 

 metrically into a multitude of linear particles aggregated 

 into discoid bundles beset with vibratile cilia, which move 

 about within their cells and soon become decomposed 

 into their component corpuscles. Each of these cor- 

 puscles has a linear body, thicker at its posterior end, and 

 furnished with two long cilia. The female cell, when 

 fertilized, gets a smooth envelope, and then a thicker one, 

 beset with conical-pointed processes, and the contained 

 chlorophyll gives place, as in Palmogloea, to starch and 

 a red or orange coloured oil. It appears that the Volvox 

 stellatus and V. aureus are only phases of the Yolvox 

 globator. 



The Desmidiacese are minute green algae inhabiting 

 fresh-water pools or slow running streams, never those 

 that are muddy. They are free unicellular plants, some- 

 times triangular, sometimes cylindrical, crescent or bow- 

 shaped, smooth or spined. So varied are their microscopic 

 forms that a description would be tedious. In plants of 

 such extreme minuteness, the only means of ascertaining 



