ALG.E. 



rolling along among Conferva. The greenish zoospore- 

 like bodies of this Alga have one cilium only, and 

 arise from a common centre by a narrowing of the base 

 (%. 14). 



In Gonium pectordle (fig. 11 a) the green bodies, 

 which are sixteen in number, and furnished each with 

 two cilia, are grouped into a flat square plate ; and in 

 the very minute Gonium tranquil' lum (fig. 11 c) these 

 bodies are also sixteen in number, and arranged in a 

 tabular form, but are without cilia. 



SIPHONA'CE^E. The structure of this family may be 

 illustrated by the genus Vaucheria, of which two or 

 three species are common on damp ground or in 

 freshwater pools, forming a green layer. At first 

 sight, the filaments of which the little plants consist 

 appear like those of a stout Conferva ; but on close 

 examination they are found to be branched, and not 

 jointed, consisting of a single cell from end to end 

 (PL VI. fig. 26). The reproduction is effected by 

 the agency of two kinds of organs, antheridia 

 and capsules (sporangia), situated near each other 

 (fig. 26 a) on the walls of the filaments, of which they 

 are protrusions or outgrowths their cavities being 

 separated from that of the filament by a partition 

 or septum. The antheridia produce spermatozoa, 

 and the sporangia each a spore, the one fertilizing the 

 other in the ordinary manner. In addition to this 

 method of fructification, zoospores are also produced 

 the ends of the filaments becoming swollen, the con- 

 tents cut off by a septum, and forming single large 

 zoospores covered with cilia, the farther development 

 of which resembles that occurring in the Confervacese. 



OSCILLATORIA'CE/E. The members of this family 

 are commonly found in stagnant water or on shaded 

 damp ground, . especially in the cold seasons of the 

 year, forming green strata or masses. 



Oscillatoria autumndlis (PL VI. fig. 1) occurs every- 

 where upon damp shaded banks of ditches, espe- 



