GENERATION. 



[ 353 ] 



GEPHYPJA. 



Strictly speaking, the term 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. (Ray 

 Soc. 1845) ; Owen, Parthenogenesis, and Ann. 

 N. H. 1851, ii. 59; A. Thomson, Cycl. An. 

 iv. Suppl. ; Braun, Rejuv., Ray Soc. 1853 ; 

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

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

 241 ; Huxley, Inv. and Verteb. ; Leuckart 

 (Ceddomyia "larva), Ann. N. H. xvii. 1866, 

 161; Sachs, Sat. 227; Nicholson, ZooL 

 1878, 33. 



GENERATION, SPONTANEOUS; some- 

 times called equivocal generation, epige- 

 nesis, or heterogeny. 



The doctrine of spontaneous generation 

 was considered to have become a matter of 

 history. We 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 true 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, Sieb. undKoll. Zeits. iii. 68; Reissek, 

 Ber. Wien, 1851 ; Pineau, Ann. Sc. Nat., 

 ZooL 1845, 1848; Pasteur, Compt. Rend. 

 1860, li. 348, 675, and 1861, Hi. 1142; 

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

 1864 ; Bastian, Beginnings of Life, 1872 ; 

 Evolution of Life, Med. Press and Circular, 

 1872 ; Tyndall* Putrefaction, 1881. 



GENICULA'RIA, De Bary. A genus 

 of Desinidiacese. 



Char. Cells cylindrical, elongate, neither 

 constricted nor incised, united into long 

 filaments. 



Fig. 278. 



Endochrome forming 2 or 



spirals (left-handed). Conjugating joints 

 geniculate. 



G. spirotania (PI. 51. fig. 36). Cells 

 slightly expanded at the ends, cell-walls 

 rough. Frankfort. 



BIBL. De Bary, Conjug. 77 ; Rabenhorst, 

 Fl. Alg. iii. 156; Pritchard, Inf. pi. 3. fig. 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. 



G. 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. subterraneus is phospho- 

 rescent. See MYRIAPODA. 



GEOR'GIA, Ehrh. A 

 genus of Mniaceous Moss- 

 es, called, from the four 

 teeth of the peristome, 

 Tetraphis and Tetrodon- 

 tium ; but these names are 

 of later date thanEhrhart's 

 (1780). G. Mnemosyne 

 presents, besides its male 

 and female inflorescence, 

 a peculiar form of terminal 

 leafy bud (fig. 278), which 

 produces stalked gemmae 

 in the interior. In the 

 figure, numerous arche- 

 gonia are also shown. 



Georgia Browniana, 

 C. Miiller, = Tetraphis 

 Brown., Grev. Georgia M u emosy ne. 



G. Mnemosyne, Ehrh. A s h oot with two 



= Tetraphis pellucida, terminal leafy buds. 

 Hedw. Magn. 15 diameters. 



GEPHYR'IA, Arn. A gemis of Diato- 

 maceaa. 



Char. Fr. arcuate, attached, destitute of 

 cellulate annuli. and septa ; hoop sublamel- 

 late, finely striate. Valves arcuate, with 

 one median and several lateral costse, dis- 

 similar ; inferior with the costse disappear- 

 ing below the ends of the valve ; superior 

 with them reaching the summit. 



G. incurvata. Ichaboe and Patagonian 

 guano. 



G. media. Calif ornian guano. 



2A 



