GERANIUM. 



[ 351 ] 



GILLS. 



G. TelfairicB. Mauritius. 



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

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



GERA'NIUM. The sepals of the com- 

 mon wild Geraniums and the garden Pelar- 

 yonia form pleasing objects when dried and 

 mounted in Canada balsam, the cells con- 

 taining regularly arranged raphides (Que- 

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



GER'DA, 01. & L. A genus of Infuso- 

 ria, fam. Vorticellina. 



Char. Sessile, resembling Scyphidia, 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. Infus. 117 ; Kent, 

 Inf. 657. 



GERMINAL VESICLE OF ANIMALS. 

 See OVUM. 



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- 

 masses which exist before impregnation 

 (Tulasne is doubtful whether before) in the 

 embryo-sac of Flowering Plants. In most 

 cases 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 suspensor, 

 which is cut off by septa into several cells, 

 the last of which usually becomes the 

 embryonal vesicle or embryo-cell, which is 

 then developed into the embryo (fig. 192, 

 page 280). See OVULE and EMBRYO. 



GERMINATION. The act of develop- 

 ment of a seed or spore into a new plant. 

 The phenomena attending the germination 

 of all the Cryptogamic plants require the 

 aid of the microscope for their investiga- 

 tion, and are in most instances highly in- 

 teresting and important in a physiological 

 point of view. For particulars, see the 

 classes of Flowerless Plants. 



GER'RIS, Latr. A genus of Hemipte- 

 rous (Heteropterous) Insects, of the family 

 Hydrometridae. 



Gerris lacustris is everywhere seen skim- 

 ming the surface of water. It has the basal 

 joint of the antennae longest, the four hind 

 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. 



Telia rivulorum, with the basal joint of 

 the antennas longest, the legs of moderate 

 length and equally apart, and Hydronwtra 

 stagnorum, with the first and second joints 

 of the antennas 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 anterior tarsi of Telia, minute mem- 

 branous retractile lobes have been described. 



BIBL. Westwood, Introd. ii. 467, and 

 Syn. 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 



Fig. 279. 



Gigartina pistillata. 



Transverse section of the 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 

 frolri the branchial artery, which ascends 



