CtASTROCH.ETA. 



[ 3ol ] 



GENEHATIONS. 



NiTiULATJiACEi. Peridium dehiscent, and 

 then fonuinfr a cup or upst, containing one 

 or many globose, oval or discoid concep- 

 tacles, lined with iilanients bearing spores. 

 Btbl. See the Families. 

 GASTROCILE'TA, Duj.— A genns of 

 Infusoria, of the family Enchelia (Uuj.). 



Char. Body oval, with one side convex, 

 the other being traversed by a longitudinal 

 furrow, which is furnished' with vibratile 

 cilia, priucipallv at the ends. 



G.fssa (PI. 3] . fig. 7). Body semitrans- 



parent, colourless, oval, ti-micated in front, 



with a very minute blunt point at the 



middle of the posterior margin, convex and 



smooth above. Freshwater; length 1-400". 



BiBL. Duiardin, Infus. p. 38.5. 



GAUDRVI'NA, D'Orb.— a Textularian 



Foraminifer, having the early chambers 



arranged triserially, as in a Vei-neuilma, 



makino; the sheU three-keeled at first ; but 



it subsequently becomes compressed and 



•wrinkled, the' chambers being alternate 



with biserial growth, as in Texfidaria. The 



aperture is usually, as in Texfidaria, a slit 



on the inner wa'U of the chamber ; but it 



niav be almost terminal and somewhat 



rounded and pouting, thus passing into_.He- 



terostomeUa. Some Gaudryince. are twisted 



and Buliminoid. Fossil and recent. PI. 23. 



fig. 48, G. pvpoidcs, D'Orb., in the Chalk. 



BiBL. D'Orb. For. Foss. Vim. ; Parker & 

 Jones, Annals N. H. ser. 3, xi. 127. 



GELATINE.— This chemical proximate 

 principle constitutes the basis of the various 

 forms of connective tissue, as existing in 

 the true skin, areolar tissue, tendon, liga- 

 ments, the swimming-bladder of fishes 

 (isinglass) ; also of bone &c. 



It possesses no microscojiic characters ; 

 it forms a most valuable vehicle for the 

 colouring-matters of liquids for injection. 



GELID'IUM, Lamx.— A genus of Cry- 

 ptonemiacese (Florideous Algse), of which 

 one species {G, corneum) is very common 

 on our shores. It has a red, pinnated, 

 homy frond, from two to six or eight inches 

 high ; very variable in the appearance of 

 its pinnate subdivisions; both spores and 

 tetraspores are found on the ramules, the 

 former in faveUidia immersed in swollen 

 ramules. 



BiBL. ITaiweT, Mar. Alg. 137, pi. 17 B, 

 Fhyc. Brii. pi. 53. 



GEMELLA'PJA, Sav. — A genus of 

 Cheilostomatous Polyzoa, of the order In- 

 fundibulata, and family Gemellariid* 

 (Eucratiidse, H.) 



G. lorictdata (PI. 86. fig. 26). CeUs in- 

 versely conical, obliquely truncate. Com- 

 mon a few fathoms Ijclow low water-mark. 



BiBL. That of the family. 



GEMELLA'RIID/E.— A family of Chei- 

 lostomatous Polyzoa, of the order Infundi- 

 bulata. 



Distinguished by the unjointed zoary, 

 and the cells being opposite in pairs. Two 

 genera : 



GemeUaria. Cells jointed back to back, 

 all the pairs facing the same way ; orifice 

 oval, oblique ; no birds'-heads (PI. 36. 

 fig. 26). . . 



Notamia. Each pair of cells ansmg 

 from the next pair but one below it by 

 tubular prolongations ; pipe-shaped birds'- 

 heads above each pair (PI. 36. fig. 21). 



BiBL. Johnston, Br. Zooph. 293 ; Busk, 

 Mar. Polyzoa, 34 ; Gosse, Mar. Zool. ii, 14 ; 

 Hincks, Polyz. 17. 



GEMMiE. — This term is applied to those 

 cellular structures, formed in Flowerless 

 Plants, which become detached, and repro- 

 duce the individual independently of the 

 spores. 



GEMMULI'NA, D'Orb. See Bige- 



NEEINA. 



GENERATIONS, alternation of.— 

 The ordinary plan upon which the repro- 

 duction of animals is elFected, viz. that of 

 sexes, involving the action of the spermatic 

 secretion upon the ova, and the subsequent 

 series of changes ultimately giving rise to 

 new individuals resembling the parents, is 

 in some instances departed from ; and the 

 embryos of certain animals, after their escape 

 from the ova, do not become directly de- 

 veloped into individuals resembling the 

 parents, but produce a new, larval kind of 

 being, which produces generations of the 

 same larval or other kinds, the last of which 

 resemble the original parents. 



"While, therefore, in animals reproduced 

 by the ordinary sexual process, the new in- 

 dividuals resemble each other, or differ only 

 in sex, in those which produce these alter- 

 nate or intermediate generations the new 

 individuals differ from the parents and even 

 from each other, until the last of the series 

 returns to the state of the first parents. 

 This mode of reproduction has received the 

 above name, from ~ the alternation of the 

 larval generations with the ordinary sexual 

 form. 



Many instances of this process are men- 

 tioned under the heads of the Classes &c. 

 in which they occur ; as under Acaxeph^, 



