GENERATION. 



[ 3.>3 ] 



GEPIIYllIA. 



Strictly speaking, the torm alternation of 

 generations is incorrect ; the process really 

 consisting of an alternation of reproduction 

 by gemmation, with that by sexual repro- 

 duction. 



BiBL. Steenstrup, Altern. of Gen. {Bay 

 Soc. 1845) ; Owen, Parthowgcm'sis, and Ann. 

 N. 11. 18.")1, ii. 5i); A. Thomson, Cycl. An. 

 iv. Suppl. ; liraun, Rejuv., Hay Soc. 1853 ; 

 Heufrey, Ann. N. H. 2 ser. ix. 441; Radlko- 

 fer, Befrucht. 1857, Ann. X. H. 2 ser. xx. 

 241 ; Huxley, Inv. and T'erteb.; Leuckart 

 {Cecidomyia larvce), Ann. N. H. xvii. 18G6, 

 IGl ; Sachs, Bot. 227; Nicholson, Zool. 

 1878, 3.3. 



GENERATION, spoxtaneous ; some- 

 times called equivocal generation, epige- 

 uesis, or heterogeny. 



The doctrine of spontaneous generation 

 was considered to have become a matter of 

 history, ^^'e noticed under Air (p. 24), the 

 experiments which were supposed to have 

 negatived the idea that microscopic plants 

 and animals derive their origin from the 

 direct transformation of decaying animal 

 and vegetable remains. We have also there 

 stated the modes by which the lower forms 

 of organic life, most commonly found in de- 

 composing infusions, propagate with extra- 

 ordinary rapidity. More recent experi- 

 ments have shown conclusively that this 

 doctrine is untenable. 



The supposed occurrence of particular 

 species of Entozoa within the bodies of 

 other animals, not to be found in any other 

 situations, was formerly considered to find 

 a ready explanation in the doctrine in ques- 

 tion. Later investigations, however, have 

 proved that these supposed species are larval 

 or other forms of tiue species of this Class, 

 which do not attain their perfect develop- 

 ment on account of their not existing in a 

 suitable locality. 



BiBL. Schultz, Fogg. Annal. xli. 184; 

 Helmholtz, Jn. prak. Chem. xxxi. 429 ; 

 Gross, tSieb. unclKoll. Zeits. iii.G8; Reissek, 

 Ber. Wien, 1851 ; Pineau, Ann. 8c. Nat., 

 Zool. 1845, 1848; Pasteur, Compt. Bend, 

 1860, U. 348, 675, and 1861, lii. 1142; 

 Pouchet, Heterogenie, 1859 ; id. Nouv. Exp. 

 1864 ; Bastian, Begimiinys of Life, 1872 ; 

 Evolution of Life, Med. Press and Circular, 

 1872: Tvndall', Putrefaction, 1881. 



GENICULA'RIA, De Bary.— A genus 

 of Desmidiaceae. 



Char. Cells cylindrical, elongate, neither 

 constricted nor incised, united into long 

 filaments. Eudochrome forming 2 or 3 



spirals (left-handed). Conjugating joints 

 geniculate. 



a. spirota'uia (PI. 51. iig. 36). Cells 

 slightly expanded at the ends, cell-walls 

 rough. Erankfort. 



BiBL. De Barv, Conjug. 77 ; Rabenhorst, 

 Fl. Alg. iii. 156; Pritcliard, Inf. pi. W. tig. 31. 



GEO'DIA, Lamk. — A genus of marine 

 sponges. Distinguished by the rounded 

 form, the solid structure permeated by 

 sinuous canals, and the solid external crus- 

 taceous covering formed of globules of silex. 



O. Zetlandica. Deep water. 



BiBL. Bowerbank, Brit. Spong. ii. 4o. 



GEOLOGY. — The microscopic investiga- 

 tion of geological products is treated of 

 under Rocks. 



GEOPHTLUS, Leach. — A genus of 

 Chilopodous Myriapoda. 



G. longicornis, with the body brownish- 

 yellow, slender, consisting of more than 40 

 joints, is common in garden-mould, under 

 flower-pots, &c. G. subterrnneus is phospho- 

 rescent. See Myriapoda. 



GEOR'GIA, Ehrh.— A Fig. 278. 

 genus of Muiaceous Moss- 

 es, called, from the four 

 teeth of the peristome, 

 TetrapJiis and Tetrodon- 

 tium ; but these names are 

 of later date thanEhrhart's 

 (1780). G. Mni'inos^jne 

 presents, besides its male 

 and female inflorescence, 

 a peculiar form of terminal 

 leafy bud (fig. 278), which 

 produces stalked gemmae 

 in the interior. In tlie 

 figure, numerous arche- 

 gouia are also shown. 



Georgia Browniana, 

 C. Mliller, = Tetr aphis 

 Broion., Grev. 



G. Mnemosyne, Ehrh. 

 = Tetraphis ^Je//«ciV/rt, 

 Hedw. 



GEPHYRTA, Arn 

 macese. 



Char. — Fr. arcuate, attached, destitute of 

 cellulate annuli and septa ; hoop sublanud- 

 late, finely striate. Valves arcuate, with 

 one median and several lateral costae, dis- 

 similar ; inferior with the costse disappear- 

 ing below the ends of the valve ; superior 

 with them reaching the summit. 



G. incur vata. Ichaboe and Patngonian 

 guano. 



Georgia Muemosyne- 



A shoot with two 

 terminal leafy buds. 



Magn. 15 diameters. 



-A genus of Diato- 



G. media. 



Californian guano. 



2 a 



