GERANIUM. 



[ 351 ] 



GILLS. 



G. Telfairm. Mauritius. 



BiBL. Arnott, Qu. Micr, Jn. viii. 20 ; 

 Greville, Micr. Tr. 1866, 77, 122 (tig.)- 



GERA'NIUM.— Tile sepals of the com- 

 mon wild Geraniums and the garden Pelar- 

 gonia form pleasing objects when dried and 

 mounted in Canada balsam, the cells con- 

 taining regularly arrani;ed raphides (Que- 

 kett, Ann. N. H. 1846,'xviii. 82). 



GER'DA, CI. & L.— A genus of Infuso- 

 ria, fam. Vorticellina, 



Char. Sessile, resembling Sqfphidia, but 

 distinguished by the absence of the pos- 

 terior sphincter or sucker, 



G. glans (PI. 52. fig. 2). — Body elongate, 

 cylindrical or clavate behind ; contractile 

 vesicle posterior, continued into a long ves- 

 sel. Freshwater. 



BiBL. Clap. & Lachm. Infiis. 117 ; Kent, 

 Inf. 657. 



GERMINAL VESICLE of Animals. 

 See Ovusr. 



GERMINAL VESICLE of Plants.— 

 This structure, the existence of which is 

 now universally admitted by physiological 

 botanists, is the germ of the future plant, 

 formed from one of the protoplasmic germ- 

 massesi which exist before impregnation 

 (Tula sue is doubtful whether before) in the 

 embryo-sac of Flowering Plants. In most 

 cages' three masses are originally produced, 

 as in Orchis (PI. 47. fig. 4) ; and in rare 

 instances two of these are fertilized, and two 

 embryos produced in one seed; sometimes 

 only one exists, and ordinarily only one is 

 fertilized. This becomes at first elongated 

 into a cellular filament called the sxspeiisor, 

 wliich is cut oft' by septa into several cells, 

 the last of which usually becomes the 

 embryonal vesicle or embrgo-cell, which is 

 then developed into the embryo (fig. 192, 

 pa'^e 280). See Ovule and Embryo. 



GERMINATION.— The act of develop- 

 ment of a seed or spore into a new pi int. 

 The phenomena attending the gerrainatim 

 of all the Cryptogamic plants require the 

 aid of the microscope for their investiga- 

 tion, and are in most instances highly in- 

 terest ii^ig and important in a physiological 

 point of view. For particulars, see the 

 classes of Flowerless Plants. 



GER'RIS, Latr.— A genus of ITemipte- 

 rous (Ileteropterous) Insects, of the family 

 HydronietridfB. 



Gerris lacitstris is everywhere seen skim- 

 ming the surface of water. It has the basal 

 joint of the antennas longest, the four liind 

 legs very long and at a great distance from 



the fore legs. The legs do not possess any 

 special structure by which they are enabled 

 to repel the water, beyond a number of 

 short hairs. 



Velia rifulorum, with the basal joint of 

 the antennae longest, the legs of moderate 

 length and equally apart, and Hgdromi-tra 

 stagnoruin, with the first and second joints 

 of the antennfe short, the third being the 

 longest, are allied members of the same 

 family, and are commonly met with on the 

 surface of pools, &c. The elegantly sculp- 

 tured eggs, and the curiously placed eyes of 

 Hydrometra, are interesting objects. 



In the anteriortarsi of Velia, minute mem- 

 branous retractile lobes have been described. 



Bibl. Westwood, Ixfrod. ii. 4G7, and 

 Si/n. 119; Douglas and Scott, Brit. Hemipt. 

  GIGAR'TINA, Lamx.— A genus of Cry- 

 ptonemiaceae (Florideous Algae), with car- 

 tilaginous irregularly-divided fronds, the 

 internal substance of which is composed of 

 rather lax tissue, the outer of dichotomous 

 filaments perpendicular to the surface, 

 strongly united by their moniliform termi- 

 nations (fig. 279). Four British species are 



Gigartina iiistillata. 



TransTerse section of tlie frond. 



Magnified 50 diameters. 



known, growing from 2 to 6 inches high, 

 of a dull purple colour. Reproduced by 

 spores (in favellidia) and tetraspores scat- 

 tered among the peripheral filaments. 



G. acicularis (PI. 4. fig. 17). 



Bibl. Harvey, Mar. Alga;, 139, pi. 17 C ; 

 Greville, Alg. Brit. 146, 147, pi. 16. 



GILLS OF Fishes. — These organs form 

 beautiful and favourite injected objects. 

 They must be injected from the heart, or 

 from the branchial artery, which ascends 



