AEGA3 : THEIR STRUCTURE AND MODE OF REPRODUCTION. 29 
cells collected into angular or tabular bodies, tbeir motion 
being caused by fine threads or cilia of protoplasm, which pro- 
ject through the colourless hyaline envelope of cellulose in 
which they are enclosed ; thus differing from the more common 
“ swarm-spores ” which we shall afterwards examine, and which 
are naked or unprovided with a coating of cellulose. The 
structure and mode of reproduction of Stephanosphcera (Plate 
CVI. fig. 1) are very curious. When fully mature it is a hyaline 
ball in which lie eight or more green cells, standing vertically 
to the horizontal diameter, and connected with the enveloping 
membrane by threads of protoplasm. These cells form together 
a family which rotates on an axis. Eeproduction is effected by 
each of these cells dividing in succession into two, four, and eight 
cells ; these eight daughter-cells form a family, which becomes 
clothed with an envelope of cellulose, with cilia protruding 
through it ; and at a certain period, before the rupture of the 
outermost membrane, eight young families may be found 
moving in circles within their parent. Volvox globator is a 
pale-green globule, ^th inch in diameter, common in ponds ; 
Stephanosphcera pluvialis is found in rain-water in the hollows 
of large stones. 
The Oscillator iece are a family of obscure plants, often of 
microscopic size, consisting generally of threads of cells, and 
characterised by an apparently spontaneous undulating or ser- 
pentine motion. To this family are generally referred the 
Vibriones and Bacteria which abound in decomposing infusions 
of vegetable substances ; the difficulty of obtaining conditions 
under which they fail to be produced having given rise to the 
controversy respecting the spontaneous generation of vegetable 
organisms, which has recently attracted so much attention in 
the scientific world. They may, however, be simpler forms of 
other algae, or even of fungi. 
In the family of Siphoneee , and especially in its typical genus 
Vaucheria , we have a more complicated structure and mode of 
reproduction than in any of those already passed in review. 
The individuals consist always of a single cell, often much 
branched, but never divided by septa into a number of distinct 
cells ; they abound in pools, or on damp soil or mud. There 
are two distinct modes of reproduction, one sexual and one 
asexual. The latter is by the production of spontaneously 
motile zoospores, or “ swarm- spores,’* which are produced by the 
protoplasmic contents of a branch of a filament accumulating 
at the end of the branch (as represented in fig. 2 a ), and finally 
falling out. The escaped zoospore b is an ellipsoidal mass of 
colourless protoplasm containing grains of chlorophyll, and 
covered everywhere by short delicate densely crowded cilia, the 
vibratile motion of which causes the motion of the zoospore or 
