AGLAOniENIA. 



[ 22 ] 



AIR. 



Fornminifera in D'Orbigny's classification 

 (l<S:?o). It may be said to comprise Cor- 

 7ni.spira, MUiola (subgenera Unihcidhia, 

 Bihmdina, Trilocvlina, Qiiingueloeuh'na, Spi- 

 rnlocn/hui, Cnicilocnlina), Ilaucrinn, and 

 Fahtdaria, members of the family 3Iiliolida, 

 as established by Car] enter. The peculiar 

 ball-of-thread-like folding of the segments, 

 "whence the name, is constant in the three 

 last-named genera ; but in CoruN.-^pira it is 

 merged in a discoidal spire at an early stage 

 of growth. 



BiBL. D'Orbigny, Foratn. Cnha, p. 145 ; 

 Foram. Canaries, p. 140; Foram. Americ. 

 p. 68 ; For. Foss. Vienn. p. 255 ; AYilliam- 

 son, Brit. Foram. p. 78, &c. ; Carpenter, 

 Int. Foram. p. GG. 



AGA'VE. See Fibeotjs Structuees. 



AGLAOPHE'NIA, Lamx (Pfr.).— A 

 genus of Polypi, of the family Plumula- 

 riidse. It consists of I'limiularia crixfuta, 

 myriop]i;iIh(m, and pennatiila (Johnston). 

 See Plumulauia. 



BiBL. Iliucks, Brit. Hydr. Zooph. p. 284, 

 pis. 63 & 64. 



AGLAOS'PORA, De Notaris.— A genus 

 proposed for Sjiha-ria profvsa, on account of 

 the a'ici containing only 4 sporidia ; but 

 Tulasne has extended it to some species 

 with eight sporidia, on account of the rela- 

 tion of the pycnidia to the perithecia. The 

 brown spores of A. profiisa, which is not 

 uncommon on Rohinia pseudacacia, are 

 beautiful microscopic objects. 



BiBL.. Tulasne. Sel. Fimf/. Carp. ii. p. 158. 



AGO'NIUM, CErst.— A genus of Cou- 

 fervoid Alg;is, fam. Oscillatoriaceee. 



Char. Filaments very slender, rigid, 

 flexuous, tufted, jointed ; a single sporidium 

 in each joint. 



A. ctntrale (PI. 3. fig. 1). Marine ; 3- 

 5'" long; attached to stones. 



BiBL. Rabenhorst, Alg. ii. 160. 



AG'RION. — A genus of Nem-opterous 

 Insects. See LiBELLULiDiE. 



AGY'RIUM, Fr.— A genus of Lichena- 

 ceous Lichens, tribe Graphidei. 



1 sp., A. rafiim. Thalliis forming 

 whitish spots; apothecia bright red. On 

 old posts. 



BiBL. Leighton, Lieh. FL, p. 392. 



AINAC'TIS, Kiitzing.— A genus of Os- 

 cilltdoriaceous plants growing on stones in 

 alpine streams. The two known species 

 have been found in Britain. 



A. alpina. Fronds from 1-12 to 1-2" in 

 diameti'r, often confluent, formed of re- 

 peatedly dichotouious filaments, dark olive 



green, containing separate particles of car- 

 bonate of lime. Hassall, Brit. Fr. Alyce, 

 Ixv. 1. 4 ; Kutz. Tab. Fhi/c. vol. ii. pi. 63. 

 1 ; Zonotrichiu hcematites, Rabenhorst, Ala. 

 ii. 212. 



A. calcarea, Kiitz. Fronds 1-4 to 1-2" 

 in diameter, orbicular, convex, idtimately 

 confluent, sometimes greenish, often dark 

 chestnut, composed of dichotomous fila- 

 ments,.at length incrusted continuously with 

 carbonate of lime. Kiitzing, I.e. jjI. 63. 2; 

 Z. calc. Rab. ; Lithonema calcaria, Hassall, 

 tab. Ixv. fio-. 2. 



Kiitzing states that the gelatinous sheaths 

 of the filaments of yl. afpina have a spiral- 

 fibrous structure. See Spieai, Stetc- 



TUEES. 



AIR. — It need scarcely be remarked that 

 the air consists essentially of a mixture of 

 two gases, oxygen and nitrogen, in the pro- 

 portion by volume of about 21 parts of the 

 former to 79 of the latter, with variable 

 quantities of gaseous carbonic acid (about 

 l-2000th) and aqueous vapour. As the 

 component molecules of gases are invisible 

 with any powers of the microscope, the air 

 possesses no microscopic characters. In two 

 respects, however, the study of the air is of 

 great importance : — 1st, in regard to the op- 

 tical appearances produced by the passage of 

 light through it when contained in bodies 

 submitted to microscopic examination ; and 

 2ndly, in regard to the particles which are 

 always, in greater or less numbers, sus- 

 pended in it. 



In microscopic investigations, we meet 

 with air either existing in cells or cavities 

 in various tissues, or in the form of bubbles, 

 confined by the liquid in which the objects 

 are usually immersed. "VVhen surrounded 

 and confined by liquid, it mostly assumes a 

 spherical form, in accordance with the law 

 of hydrostatics, that the pressure of fluids 

 is equal in all directions; sometimes the 

 spherical form is exchanged for that of a 

 compressed or oblong spheroid, the result of 

 the pressure of the glass slip covering the 

 object. When confined in cells or cavities, 

 it assumes the form of these. It is in ge- 

 neral easily recognized by transmitted light 

 from the smooth and even darkness or 

 shading given to its margins, whilst in the 

 centre it appears luminous and clear. Some- 

 times the dark margins of air-bubbles have 

 a pale purjjlish-yellow, blue or greenish 

 tinge. By reflected light, of course, no dark- 

 ness is produced, but it then appears vitre- 

 ous and shining, in co^isequence of the re- 



