GERANIUxM. 



[ 289 ] 



GILLS. 



GERxlNIUM. — In this genus, and appa- 

 rently in the rest of the Nat. Ord. Gera- 

 niaceae, the sepals are remarkable for the 

 cells containing numerous raphides regularly- 

 arranged. They may be observed in the 

 common G. Rohertianum and in the garden 

 Pelargonia. The sepals of the common wild 

 Gerania form pleasing objects when dried 

 and mounted in Canada balsam. 



BiBL. Quekett, Ann. Nat. Hist, xviii. 

 p. 82. 



GERMINAL VESICLE of Animals. 

 See Ovum. 



GERMINAL VESICLE, of Plants. 

 — This structure, the existence of which is 

 denied by Schleiden and Schaeht, but 

 affirmed by Amici, Mohl, Miiller, Henfrey, 

 Hofmeister, Tulasne, &c., is the germ of the 

 future plant, formed before impregnation 

 (Tulasne is doubtful whether before) in the 

 embryo-sac of Flowering Plants. In most 

 cases three are originally produced, as in 

 Orchis (PI. 38. fig. 4), and in rare instances 

 two of these are fertilized, and two embr\os 

 produced in one seed ; sometimes only 

 one exists, and ordinarily only one is ferti- 

 lized. 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 ordinarily becomes the 

 embryonal-vesicle or embryo-cell, which be- 

 comes developed into by the embryo (fig. 195. 

 page 225). 



GERMINATION.— The act of develop- 

 ment of a seed or spore into a new plant. 

 The phsenomena attending the germination 

 of all the Cryptogamic plants require the aid 

 of the microscope for their investigation, and 

 are in most instances highly interesting and 

 important in a physiological point of view. 

 For particulars, see under the classes of Flow- 

 erless Plants. 



GERRIS, Latr. — A genus of Hemipterous 

 (Heteropterous) Insects. 



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 di- 

 stance 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. 



Celia rivulorum, with the basal joint of 

 the antennae longest, the legs of moderate 

 length and equally apart, and Hydrometra 

 stagnorum, with the first and second joints 

 of the antennae short, the third being the 

 longest, are allied members of the same 



family, and are commonly met with on the 

 surface of pools, &c. 



In the anterior tarsi of Celia, minute mem- 

 branous retractile lobes have been described. 



BiBL. Westvvood, Introduction, Sfc. 



GIGARTINA, Lamx.— A genus of Cry- 

 ptonemiaceae (Florideous Algae), with cartila- 

 ginous, 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 terminations (fig. 283). 



Fig. 283. 





Gigartina pistillata. 



Transverse section of the frond. 



Magnified 50 diameters. 



Four British species are known, growing 

 from 2 to 6 inches high, of a dull purple 

 colour. Reproduced by spores (in favellidia) 

 and tetras))ores scattered among the peri- 

 pheral filaments. 



BiBL. Harvey, British Marine Alga, 

 139. pi. 17 C; Greville, Alg. Brit. pp. 146, 

 147. pi. 16. 



GILLETT'S CONDENSER. See Con- 

 denser. 



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 from the 

 heart much in the same manner as the 

 pulmonary artery ascends from the heart of 

 the higher animals. It may be remarked 

 that the heart of fishes is situated much 

 nearer to the anterior end of the body than 

 in the Mammalia. 



BiBL. Stannius, Lehrb. d. Vergl. Anat.; 

 Lereboullet, Anat. Compar. de FAppar. 

 Respir. ; Hyrtl, Med. Jahrbiich. d. (Ester. 

 St. bd. 24 ; Owen, Hunterian Led. ii. 



GILLS OF Insects, or branchiae. — 



u 



