PLANORBULINA. 



[ 605 ] 



PLATYZOMA. 





decomposing vegetable matter ; length I 

 1-250". 



BIBL. Vuj.Inf. 568. 



PLANORBULI'NA, D'Orb. A genus 

 of Hyaline Foraminifera. Shell spiral, 

 coarsely porous, subnautiloid or outspread, j 

 often parasitic; haying from 15 to 200 

 chambers, with single septa and slight i 

 rudiments of the canal-system. Aperture j 

 sometimes produced and lipped. Compla- j 

 nate (PI. mediterranensis, PI. 24. fig. 10) ; 

 plano-convex, Truncatidina (T. lobatula, , 

 PI. 24. fig. 9) ; rotaliif orm (PI. Haidingerii, \ 

 PI. 24. fig. 6 ; PL veneta, fig. 12) ; or sub- j 

 uautiloid (Anomalina and Planulina). 

 Smooth ; limbate (Planulina) ; or granulate. ! 

 In all seas ; fossil in the Carboniferous, ; 

 Lias, and later formations. 



BIBL. Carpenter, For. 206 ; Parker and I 

 Jones, Phil. Tr. civ. 379. 



PLANTA'GO. The common plaintain ; i 

 its leaf and hairs furnish excellent exam- 

 ples of Cyclosis. See Carpenter, Microscope, j 

 p. 431. 



PLANULA'RIA, Defrance. A notice- 

 able group of delicate, elongate, flattened 

 Cristettarice, connecting the nautiloid with | 

 the marginuline varieties, come under this 

 name. Recent and fossil. 



BIBL. Parker and Jones, Ann. N. H. 3. 

 v. 114 (crepidula) ; xii. 215 ; 4. viii. 166. 



PLANULI'NA, D'Orb. A subgenus of 

 Planorbulina j flat, discoidal, subsymmetri- 

 cal, and with raised margins and septal 

 lines (limbate). Recent and fossil. 

 BIBL. Carpenter, Introd. For. 207. 

 PLASMO'DIUM. A sponge-like net- 

 work, formed by the union of the pseudo- 

 podia of amoeboid bodies. 



PLAS'TIDS. The simplest living forms, 

 and the most elementary parts of tissues, j 

 consist of (1) small particles and masses of i 

 protoplasm without a nucleus or any trace ! 

 of structure (our protoplasts, 1856), (2) of | 

 similar portions of protoplasm in which a 

 nucleus has been differentiated. The first 

 group Hackel terms Cytodes, the second 

 cells ; and both are grouped under the head 

 of Plastids. 



The cytodes, or the protoplasmic masses 

 without a nucleus, are : 



Gymnocytodce, or naked cytodes. Such \ 

 are the freely moving Monera, the non- | 

 nucleated plasmodia of Myxomycetts, and j 

 of several other Protista, the amoeboid 

 germs of the Gregarince proceeding from 

 the pseudo-naviculee, &c. 



Lepccytoda, or covered cytodes. These 



are plasma-masses without a nucleus, en- 

 closed in an entire or incomplete membrane 

 or shell. For example, the encapsuled 

 resting condition of many jLepo?nonera,mimy 

 Siphoncea, and numerous other lower plants, 

 and the so-called non-nucleated cells of 

 many, higher plants and animal tissues. 



The cells or cyta are plasma-masses with 

 a nucleus, and are divided into : 



Gymnocyta, naked cells. Such are the 

 naked plasma-masses with a nucleus, but 

 without a membrane or shell ; for example, 

 the true Apiosba, the naked zoospores of 

 Algae, the eggs of Siphonophora, and other 

 animals, the colourless blood-cells, many 

 nerve-cells, &c. 



Lepocyta, or covered cells. Such are the 

 cells of animals, plants, and tissues with 

 nuclei and cell-walls. See PROTISTA, 

 CYTODE. 



BIBL. Hackel, Biol. Studiett, H. i. ; Qu. 

 Mic. Jn. 1869, 331 ; Hallier, Plastids, 1878. 



PLAT'INUM. The sodio-ehloride of 

 platinum crystallizes in prisms and plates 

 which polarize light; while the potassio- 

 chloride of platinum yields several forms, 

 which do not polarize light. This reaction 

 of the soda-salt has been proposed as a 

 means of distinguishing soda from potash, 

 or detecting minute quantities of the 

 former. 



BIBL. Andrews, Chem. Gaz. 1852, x. 378. 



PLATYCE'RIUM, Desv. A genus of 

 Acrosticheae (Polypodiaceous Ferns). 5 

 species ; tropical. (Hooker, Syn. 425.) 



PLATYCHE'LIPUS, Br. A genus of 

 Copepodous Entoinostraca. P. littoralis] 

 brackish water. (Brady, Copep., Ray Soc. 

 ii. 102.) 



PLAT YC 'OLA, Kt. Like Vaginicola, 

 but the sheath decumbent, and attached by 

 one side. Freshwater; several species. 

 (Kent, Inf. 731.) 



PLATYG'RAPHA, Nyl. A genus of 

 Graphidei (Lichenaceous Lichens). P. ri- 

 mata, on ash trees, rare. (Leightoii. Lich. 

 Flor. 388.) 



PLATYS'MA, Hoffm. A genus of 

 Ramalodei (^Lichenaceous Lichens). 10 spe- 

 cies, on rocky mountains &c. (Leighton, 

 Lich. Fl. 93.) 



PLATYTHE'CA, St. A genus of Fla- 

 gellate Infusoria. Ovate, with a decumbent 

 rugose carapace ; flagellum single : length 

 1-1200" ; on Lemna. (Kent, Inf. 262.) 



PLATYZO'MA, Br. A genus of Glei- 

 cheuiaceous Ferns. P. microphyllum. Aus- 

 tralia. (Hook. Syn. 11.) 



