OVUM. 



[ 571 ] 



PACHYGNATHUS. 



1880; His,Menschl.Emb)yo,lS80; Reichert, 

 Menschl. Frucht. 1873 ; Girdwoyn, Mai d. 

 CEufs (fish), 1880. 



OVUM OF PLANTS. See OVULE. 



OXALATES. See the bases. 



OXYR'RHIS, Duj. A genus of Flagel- 

 late Infusoria, belonging to the family 

 Thecamonadina. 



Char. Body ovoid - oblong, rugose, ob- 

 liquely notched in front and prolonged into 

 a point ; several flagelliform filaments (two, 

 Kent) arising laterally from the bottom of 

 the notch. 



O. marina (PI. 31. fig. 54). Body colour- 

 less, subcylindrical, rounded behind; ma- 

 rine ; length 1-500". 



BIBL. Dujard./n/. 347; Pritchard, Inf. 513. 



OXYT'RICHA, Bory, Ehr. A genus of 

 Hypotrichous Infusoria, of the family Oxy- 

 trichina. 



Char. Closely resembling Stylonychia ; 

 but the front of the body not produced. 



O. pellionella, E. (PI. 31. fig. 52). Body 



whitish, smooth, slightly depressed, equally 

 rounded at the ends, often somewhat broader 

 in the middle ; head not distinct ; mouth 

 ciliated; tail with bristles. Freshwater: 

 length 1-720 to 1-280". 



O. ffibba E. (PI. 31. fig. 53). Body white, 

 lanceolate, obtuse at each end, ventricose 

 in the middle ; ventral surface flat, with a 

 double row of setae ; mouth large, rounded. 

 Freshwater; length 1-240". Other species. 



According to Haime 7 Oxytricha is the 

 larva of Aspidisca. 



BIBL. Ehr. Inf. 363; Duj. Inf. 416; 

 Haime, Ann. Sc. Nat. 3. xix. 109 ; Clap, et 



family of Hypo- 



Lachm. Etudes, 139 ; Kent, Inf. 786. 



OXYTRICHI'NA. A family of ] 

 trichous Infusoria. 



Char. Carapace absent; body depressed, 

 with vibratile cilia, setse, or cirri, and non- 

 vibratile styles or hooks. Movement crawl- 

 ing. Alimentary orifices two, neither ter- 

 minal. 



Genera : 



if 



Tvrov^-Tioi 

 Marginal cirri 



l\ 



I! 



/ 

 s, j 



... ) 

 ( 



The anterior part of the body not pro- 

 longed as a neck, furnished with cirri Oxytricha. 



The anterior part of the body neck-like, 

 and cove red with cirri Stichochceta. 



No marginal cirri 



/Foot-cirri in regular rows 

 J longitudinal or oblique 



(.Foot-cirri not arranged in rows , Stylonychia. 



fw,-f>, ft.toi f Foot-hooks / No dorsal bristles Euplotes. 



J oirn 1 exist i Dorsal bristles Schizopus. 



*) Cim [No foot-hooks Campylopus. 



^Without frontal cirri Aspidisca. 



BIBL. Ehr. Inf. 362 ; Pritch. Inf. 639 ; 

 Clap, et Lachm. Etudes, 168. 



OXYUR'IS, Rud. See ASCARIS. 



OY'STER (Ostrea). A genus of Lamel- 

 libranchiate Mollusca. 



The gills of O. edulis, the common oyster, 

 show the ciliary movement ; but it is not so 

 easily seen in this as in the marine mussel. 



The shells of the fry or 'embryo oysters' 

 exhibit the black cross and an imperfect 

 set of coloured rings with polarized light. 



P. 



PACHNOC'YBE, Berk. A genus of 



/TT 1 J. T1 *\ 



have an erect filiform stem, composed of 

 conjoined filaments, capitulate above, the 

 head being; pruinose (not fiocculent), with 

 crowded simple spores. The pedicels are 

 mostly brownish or blackish, the spores 

 light-coloured ; the entire plants from 1-24 

 to 1-6" high. Several species occur on 

 rotten wood, stems, &c. 



BIBL. Berk. Hook. Br. Fl. ii. pt. 2. 333; 



Ann. N. H. 2. v. 465; Fries, Sum. Veq. 

 467. 



PACHYG'NATHUS, Duges, A genus 

 of Trombidina (Acarina). 



Char. Palpi conical, last joint scarcely 

 forming a claw; mandibles stout, chelate; 

 body entire, narrowed in front ; coxae dis- 

 tant ; legs gressorial, sixth joint very long, 

 seventh very short; anterior legs longest 

 and stoutest. 



> P. velutinus (PL 6. fig. 34), the only spe- 

 cies. Found in autumn, under damp stones. 

 Hairs covering the body short, flat, and 

 curved, giving it a velvety aspect. Body 

 inflated, narrowed in front, the narrowed 

 portion with two projecting brownish eyes. 

 Insertions of the legs in two groups, not 

 far distant, or from the median line ; second 

 pair of legs shortest ; in all the sixth joint 

 very long, the seventh very short and nar- 

 row (6), as in Tetranychus, Megamerus, and 

 Raphiynathus ; claws two, large ; rostrum 

 projecting; palpi (a) short, about twice the 

 length of the labium ; mandibles very large 

 and stout at the base. Movement slow. 



BIBL. Duges, Ann. Sc. Nat. 2. ii. 54; 

 Gervais, Walck. Aptfrr. iii. 171. 



