OSCILLATORIACEJ3. [ 563 ] 



OTOGLENA. 



ceuding, enclosed in lamellated,hard sheaths, 

 concreted laterally at their bases, involved 

 in jelly. 



jRhtzonema. Sheath cellular and fur- 

 nished throughout its length with numerous 

 branched and anastomosing rootlets (?). 

 Filaments distinctly annulated, and inter- 

 rupted here and there by a connecting cell. 

 Branches in pairs, arising from a protrusion 

 of the filament. 



Fischer a. 



D. Rivulariea. Filaments distinctly arti- 

 culated, with an enlarged basal cell, 

 mostly attenuated above, connected into 

 definite or indefinite fronds ; motionless. 



Schizosiphon (PI. 8. fig. 13). Basal cells 

 globose, filaments simple, distinctly articu- 

 lated, mostly attenuated towards the apex, 

 sheathed, sheaths connate into groups, hard, 

 dark-coloured, open and expanded above, 

 and overlapping so as to form a succession 

 of ochrese which have the free borders 

 slit up into filaments or fringes ; also dis- 

 playing a spiral fibrous structure in dissolu- 

 tion. 



Physactis. Filaments whip-shaped, toru- 

 lose at the base, sheathed, sheaths simple, 

 gelatinous, collected into a globose and 

 solid, or subsequently a bullose-vesicu- 

 lar frond ; in the globose fronds the fila- 

 ments radiate from the centre, in the vesi- 

 cular fronds from the internal or lower 

 surface of the gelatinous matrix. 



Ainactis (PI. 8. fig. 15). Filaments 

 branched, jointed, with thin sheaths, col- 

 lected into a solid pulvinate frond, concen- 

 trically zoned by the dichotomous branching 

 of the filaments. Sheaths more or less 

 solidified by carbonate of lime ; sometimes 

 exhibiting a spiral structure in dissolution. 



Rwularia (PL 8. fig. 18). Filaments 

 with an oval basal cell succeeded by one of 

 cylindrical form (manubrium), the remainder 

 short, attenuated in diameter upwards (whip- 

 shaped) ; sheaths sometimes saccate below, 

 open (not fringed) above ; forming a slippery 

 gelatinous frond. 



Euactis (PL 8. fig. 16). Filaments whip- 

 shaped, with repeated ochreate sheaths, 

 forming fronds in which they radiate, and by 

 superposition of successive generations form 

 concentric layers; sheaths cartilaginous, 

 lamellated, firmly united laterally, dilated 

 upwards (funnel-shaped), decomposed into 

 a fringe at the orifice. 



Inomeria. Filaments whip-shaped, ver- 

 tical, parallel ; sheaths obscure, everywhere 



decomposed into very slender filaments ; 

 forming crustaceous fronds, becoming stony. 

 Petronema. Densely caespitose, erect, 

 somewhat regularly branched; branches free, 

 with obtuse rounded apices, and each with 

 a connecting cell at the base. Filaments 

 annulated and growing thicker upwards. 



E. Leptotricliece. Doubtful Oscillatoriace^. 

 Leptothrix. Filaments very slender, 

 neither branched, articulated, concreted, 

 nor sheathed. 



Hypheothrix. Filaments unbranched, in- 

 articulate, sheathed, interwoven into a more 

 or less compact stratum. 



Symploca. Filaments unbranched, inar- 

 ticulate, sheathed, concreted into branches, 

 conjoined at their bases; sheath a simple 

 hyaline membrane. 



OSMIC ACID. An oxide of the metal 

 osmium, obtained from platinum-ores. It 

 is a crystalline, volatile, poisonous substance, 

 soluble in water, with a powerfully irritating 

 odour. Its aqueous solution is used for 

 hardening and colouring certain animal tis- 

 sues black or dark blue, as fat-cells and 

 globules, the medulla of nerves, more slowly 

 the ganglion-cells, the connective-tissue cor- 

 puscles, Zoophytes, &c. The ordinary 

 strength is about 90 grains to a pint. 

 Small pieces of the structures should be 

 immersed in it, from hour to 24 houry, 

 then well-washed in distilled water, and 

 mounted in acetate of potash or Farrant's 

 compound. It is also useful for its remark- 

 able power of killing Infusoria, Rotatoria, &c. 

 so suddenly, that the cilia remain extended, 

 instead of being retracted and undistinguish- 

 able as with other reagents. (Ranvier, Hist, 

 teckn. ; Robin, Micr. 220 ; Frey, Mikr.} 

 OSMO'SIS. See ENDOSMOSB. 

 OSMUN'DA, Linn. A genus of Osrnun- 

 daceous Ferns, represented in Britain by 

 Osmunda regalis ^(figs. 222, 223, p. 319), the 

 Royal or Flowering Fern, as it is termed, a 

 large and handsome plant, found in damp 

 situations ; not common. 



OSMUNDA'CE^E. An order of Poly- 

 podiaceous Ferns, characterized by the broad 

 imperfect annulus on the back of the spo- 

 ranges. Genera : 



Osmunda. Sporangia on metamorphosed 

 pinnules. 



Todea, Sporangia on unchanged pin- 

 nules. 



OSTRACO'DA. See ENTOMOSTBACA. 

 OTOGLE'NA, Ehr. A genus of Rota- 

 toria, of the family Hydatinsea. 

 2o2 



