NUMMULINA. 



[ 549 ] 



ODONTELLA. 



until the decay of the organ in which they 

 exist. This happens very generally in the 

 cells of the flowers, stems, &c. of Monoco- 

 tyledons ; not uufrequently, in stems and 

 leaves they become converted into starch or 

 chlorophyll granules. In other cases they 

 have a more definite purpose; for in the 

 vesicles in which are formed the SPERMATO- 

 ZOIDS of Ferns, Mosses, Hepaticae, Chara- 

 ceee, &c., these structures appear to be pro- 

 duced by a metamorphosis of the nuclei. 



In examining supposed nuclei of plants, 

 especially those of lower cellular organiza- 

 tion, tincture of iodine should always be 

 applied, to distinguish starch-granules &c. 

 from true nuclei, which are always coloured 

 deep yellow or brownish by that reagent, 

 besides being coagulated, contracted, and 

 thereby rendered more distinct. 



BIBL. R. Brown, Phil. Mag. Dec. 1831; 

 Nageli, Zeit. iviss. Bot. (Ray Soc. 1845 & 

 1849); Mohl, Pflanzenzelle, 36, 51; Hof- 

 meister, Entsteh. d. Embryo, 1849, 7; Braun, 

 Verjunguny (Ray Soc, 1853, 175); Sachs, 

 Bot. 45 ; Strassburger, Zellenbildung, 1880. 



NUMMULI'NA, D'Orb. I A Hyaline Fo- 



NUMMULI'TES,Lamk. j raminifer of 

 the highest class. Shell lenticular, varying 

 in convexity and in size (from less than Jg- 

 to 2^ inches in diameter), composed of 

 several, overlapping, uniform, whorls of nu- 

 merous > -shaped chambers in a discoid 

 spire. These are prolonged towards the 

 umbo of each face, thus forming Alar 

 Lobes, either straight (in the Radiatce), 

 or sinuous (Sinuatce), or inosculating (Reti- 

 culates). The alae are abortive or absent, 

 and the spire therefore exposed, in Assilina 

 and Operculina, unequal and modified in 

 Amphistegina. The chambers communicate 

 bv a transverse slit at the base of the 

 septum, with smaller occasional holes. The 

 outer chamber-walls (Spiral Lamina) are 

 thin in the latest, but in the older cham- 

 bers thickened by successive layers of the 

 delicate tubuliferous shell. Over the septa 

 of the median plane (PL 24. fig. 22), and 

 where the alar septa cross and touch, the 

 tubuli being obsolete, the shell becomes 

 translucent (Pillars) ; at the outer margin 

 (Marginal Cord) also of the whorls the 

 layers of shell become translucent, and are 

 traversed by radiating and inosculating 

 tubes, continuous with canals passing be- 

 tween the two shell-layers of each septum 

 (Interseptal Canals), and with the canals 

 in the margin of the inner whorls. This 

 Canal-system carries spiral and branching 



threads of sarcode through the denser parts 

 of the shell, which, indeed, in some Polysfo- 

 meUce and Ccdcarinte appear to be secreted 

 thereby (Supplementary Skeleton). 



Nummulina is rare in the Carboniferous, 

 Jurassic, and Cretaceous, but very common 

 in the Lower Tertiary strata ; living in the 

 North, Red, and Australian seas, but small 

 (N. radiata, PL 24. fig. 21). 



BIBL. D' Archiac et Hairne, An.foss. Num. 

 Inde, 1853; Carter, Ann. N. H. ser. 2. xi. 

 161, ser. 3. viii. 320, 366 ; Parker and Jones, 

 Ann. N. H. ser. 3. v. 106, viii. p. 229 ; Car- 

 penter, Foram. 262, Microscope, 1858, 510 ; 

 Brady, Ann. N. If. ser. 4. xiii. 222. 



NYCTOTHE'RUS, Leidy. A genus of 

 Heterotrichous Infusoria, very near Playio- 

 toma. 4 species ; in the intestines of Am- 

 phibia and Invertebrata. (Kent, Inf. 579.) 



NYMPELEACE.E. See HAIBS (p. 379). 



O. 



OAT, Avena sativa (Nat. Order Grami- 

 nacese, Flowering Plants). The form of 

 the starch-corpuscles of the oat is very un- 

 like that of the other common corn-plants ; 

 they consist of numerous small polygonal 

 grains grouped together in roundish or oval 

 masses (PL 46. fig. 10). See STABCH. 



OBE'LIA=Zaom<?cfea pt. 



OBISIDA. See ARACHNIDA. 



OBJECT-GLASS, or OBJECTIVE. See 

 INTRODUCTION, p. xvi. & ANGULAR APER- 

 TURE, p. 47. 



OCEL'LI. The simple eyes or eye-spots 

 of the Invertebrata ; they are noticed under 

 the classes. 



OCHLOCH^ETE, Thwaites. A genus 

 of Chsetophoraceae. O. hystrix, on grasses 

 in freshwater and brackish ditches. 



OCHROP'TERIS, Sm. A genus of 

 Pteridese (Polypodiaceous Ferns). O. pal- 

 lens-, Mauritius. (Hook. Syn. 127.) 



OCTAVIA'NA, Tul. A genus of Gas- 

 teromycetous Fungi (section Hypogaei) dis- 

 tinguished by the sterile base of the conti- 

 nuous or cracked peridium; the easily 

 divisible byssoid frames and the fruit- 

 bearing cavities at first empty, then covered 

 with the rough spores. 



BIBL. Tul. Fung. Hyp. t. ii. f. 1 : Berk. 

 Outl. 292 ; Cooke, Handb. 355. 



OCTOSPORES. Sporangia of Fucaceze, 

 which subdivide into a cluster of eight cells. 



ODONTEL'LA, Ag. This genus of 

 Diatomacese is united with BIDDULPHIA, 

 Biddulphia (Odontelld) aurita undergoing 

 spontaneous division, PI. 19. fig. 9. 



