74 ALG.E. 



open at the sutures, and the effused contents become 

 united to form a spore or sporange, from which one 

 or more individuals are formed. These spores are 

 often elegantly spinous on the surface. 



Among the species selected for illustration is Clos- 

 terium acerosum (PI. V. fig. 9), in which the cells are 

 single, elongate, very slightly curved or lunate ; the 

 endochrome forms long bands, often containing nu- 

 merous globules or transparent vesicles. At each 

 end of the cells is a round transparent vesicle, con- 

 taining exceedingly minute granules, which exhibit a 

 trembling kind of motion. Between the cell- wall 

 and the cell-contents very fine currents may also be 

 detected, forming a circulation resembling that in the 

 hairs of Tradescantia. 



In Micrasterias rotdta (PL V. fig. 16) the cells, 

 which are single, are deeply cleft into two segments 

 at the suture, the segments being again regularly cut 

 into five lobes, which are toothed or dentate. 



In Hyalotheca dissil'iens (PL V. fig. 21) the cells 

 are united into a cylindrical filament, and are sur- 

 rounded by a very delicate gelatinous sheath. In 

 Ankistrodes'mus falcdtus (PL V. fig. 19) the cells re- 

 semble those of Closterium in shape, but are aggre- 

 gated into faggot-like bundles, and are very much 

 smaller. In the beautiful little Pediadtrum borydnum 

 (PL V. fig. 20) the cells are aggregated into a disk, 

 the marginal cells being bidentate or having each two 

 points, so that the whole resembles a star. The species 

 of Pediastrum are reproduced by the contents of each 

 cell subdividing into numerous ciliated segments or 

 zoospores, which subsequently escape in a mass from 

 the cell, ultimately losing their cilia, and reuniting 

 to form a new individual. 



In Scenedes'mus quadricauda (PL V. fig. 25) the 

 oblong cells are united, side by side, the outermost 

 cells being furnished with a bristle at each end. The 

 division of these cells takes place obliquely, so that 



