MICA. 



[ 425 ] 



MICROGONIDIA. 



dichotomous, membranous, and ribbed. M. 

 furcata is hairy beneath, and smooth above] 

 M.pubescens hairy on both sides, and larger. 

 In addition to the sporanges, these plants 

 are increased by gemmae formed in patches 

 on the attenuated lobes of sterile fronds. 



BIBL. Hook. Brit. Flor. ii. pt. 1. 131, 

 Brit. Jungermann. pi. 55. 56 & 73; Endli- 

 cher, Gen. Plant. Supp. 1. p. 1338; Hof- 

 meister, Vergleich. Untersuch. p. 10. pi. 4. 



MICA. This mineral substance, which is 

 often erroneously called talc in the shops, 

 was formerly used for covering mounted 

 objects, but is now replaced by thin glass. 

 It is, however, occasionally useful in apply- 

 ing a red heat to objects, as Diatomaceae, 

 &c., where it is required not to change the 

 position of the object. It often contains 

 crystalline and crystalloidal inorganic mineral 

 substances, as metallic oxides, &c., of in- 

 teresting appearance. 



MICRASTERIAS, Ag. A genus of Des- 

 midiacea3 (Confervoid Algae). 



Char. Cell single, lenticular, deeply divided 

 into two lobed segments; lobes inciso-dentate 

 (rarely only bidentate), and generally radia- 

 ting. 



Sporangia spherical, with stout spines (PL 

 10. fig. 12). 



Thirteen British species (Ralfs). 



M. denticulata (PL 10. fig. 11, undergoing 

 division ; fig. 12, sporangium). Cell cir- 

 cular, surface smooth ; segments five-lobed ; 

 lobes dichotomously divided, ultimate sub- 

 divisions truncato-emarginate, with rounded 

 angles. Length 1-113 . Common. 



M. rotata (PL 10. fig. 13). Cell circular, 

 smooth; segments five-lobed; lobes dicho- 

 tomously incised, ultimate subdivisions bi- 

 dentate. Length 1-91". Common. 



BIBL. Ralfs, Brit. Desmid. p. 68. 



MIGROCLADIA, Grev. A genus of 

 Ceramiaceae (Florideous Algae), containing 

 one rare British species, M. glandulosa, 

 with a dichotomously branched, filiform, 

 compressed frond 1 to 2" high, of a bright 

 rose colour. Its fructification consists of ( 1 ) 

 roundish, sessile involucrated favellse with 

 spores, and (2) tetraspores (tetrahedrally 

 arranged) imbedded in the ramules. 



BIBL. Harvey, Brit. Mar. Alg. p. 160. 

 pi. 22 B, Phyc. Brit. pi. 29; Grev. Alg. 

 Brit. t. xix. 



MICROCODON, Ehr. A _ genus of Rota- 

 toria, belonging to the family Megalotro- 

 chaea. 



Char. Eye single ; no carapace ; foot sty- 

 liform. Jaws two, each with a single tooth. 



M. Clams (PL 35. fig. 8). Body campa- 

 nulate, foot equalling or exceeding the body 

 in length. Aquatic. Length 1-288 to 1-216 . 



BIBL. Ehrenberg, In/us, p. 395. 



MICROCOLEU S, Desmaz. ( Chthonoblas- 

 tus, Kiitz.). A genus of Oscillatoriaceae 

 (Confervoid Algae), with fronds forming strata 

 on moist ground, paths, mud, &c. These 

 plants may be described as bundles of Oscil- 

 /atona-filaments enclosed in a common 

 gelatinous sheath, which is simple or irregu- 

 larly dichotomously branched, and forms 

 twisted interwoven masses. The structure 

 of the filaments appears to be identical with 

 that occurring in OSCILLATORIA, described 

 under that head; the filaments oscillate; 

 the mode of origin of the enclosing sheath is 

 obscure, but it would appear to be formed 

 of the gelatinous half- dissolved outer mem- 

 branes of the enclosed filaments. No for- 

 mation of spores or gonidia has been de- 

 scribed. M. repens, Harv. (PL 4. fig. 9 a, 

 the open end of a sheath), is very common 

 on damp paths, &c., its sheaths are branched; 

 M. anguiformis, Harv., occurs on the mud of 

 brackish pools ; its sheaths are said to be 

 simple. M. gracilis, Hassall, said to be 

 found in similar situations, has no character 

 attached to it. 



BIBL. Harvey, Brit. Mar. Alg. p. 227. 

 pi. 26 D, Phyc. Brit. pi. 249 ; Hassall, Br. 

 Freshw. Alg. p. 260. pi. 70; Kutz. Tab. 

 Phyc. i. pi. 54-58. 



MICROCYSTIS, Kiitz. A genus of Pal- 

 mellaceae (Confervoid Algae), but a doubtful 

 object, and possibly merely a resting form 

 of EUGLENA. 



BIBL. Kiitzing, Linncea, viii. p. 342; 

 Spec. Alg. p. 208, Tab. Phyc. pis. 8, 9. 



MICROGLENA, Ehr. A genus of Infu- 

 soria, of the family Monadina, E. 



Char. Tail absent; body truncated in 

 front, with a single flagelliform filament ; a 

 red eye-spot present. 



Probably the spores of Algae. 



M. punctifera (PL 24. fig. 43 a). Body 

 yellow, ovate, subconical, attenuate poste- 

 riorly,red eye-spot accompanied bya blackish 

 frontal spot (in Ehrenberg's figures, some 

 have one, some two red eye-spots). Aquatic; 

 length 1-620". 



M. monadina (PL 24. fig. 43 b). Body 

 ovate, equally rounded at both ends, bright 

 green, eye-spot red and single. Aquatic; 

 length 1-1150 to 1-620". 



BIBL. Ehrenberg, Infus. p. 25. 



MICROGONIDIA. See MACROGO- 



NIDIA. 



