FOSSOMBRONIA. 



[ 272 ] 



FROG. 



different conditions, as for example converted 

 into lignite, and the modifications of coal, or 

 with the vegetable substance almost entirely 

 removed and replaced by silex, preserving all 

 the organic forms of the tissues. The mode 

 of examining and mounting Coal, &c., is 

 given under that article. Silicified woods 

 which have been completely infiltrated and 

 solidified require to be cut into thin sections 

 and polished by the lapidary ; the friable 

 kinds, where the infiltration has merelv filled 

 the cavities of the cells and vessels, may be 

 split with a knife and mounted in balsam. 

 Examples are given in PL 1.9. figs. 29-33. 

 Fig. 32. PI. 39 exhibits concretions of silica 

 imitating structure. The stems of Palms and 

 Dicotyledonous trees are metwith completely 

 converted into siliceous blocks, sections of 

 which exhibit all the miimtise of the struc- 

 ture. 



FOSSOMBRONIA, Raddi.— A genus of 

 Pelliese (Hepaticaceae), nearly allied in the 

 character of its vegetative structure to the 

 Jungermanniese, having large, squarish, irre- 

 gularly waved leaves; the stout stems are 

 procumbent and set with purple radicles all 

 along the under side. The fruit-stalk arises 

 from the under side of the stem and turns 

 back, the perichsete is very large, and the 

 capsule bursts irregularly into four slender 

 erose valves. F. ptisilla is the Jungermannia 

 pusilla of the British Flora; found chiefly on 

 clay banks. 



BiBL. Hook. Brit. Jungerm. pi. 69, Brit. 

 Flor. ii. pt. 2. p. 117; Endlicher, Gen. Plant. 

 suppl. i. no. 472-7. 



FOVILLA. — The name applied to the 

 minute granules contained in the liquid filling 

 the pollen-cell and passing into the pollen- 

 tube of Flowering Plants. These minute 

 granules, which are of various, but altogether 

 indefinite sizes, exhibit an active quivering 

 motion, the ' molecular motion ' as it is 

 called, which is displayed in the same way 

 by all finely-divided solid substances, living 

 or dead, and is apparently dependent on 

 purely physical causes. They appear to 

 consist of starch-grains, minute globules of 

 oil, and granules of protoplasm probably 

 composed of proteine compounds. These 

 granules are exceedingly transparent in many 

 kinds of pollen when fresh, apparently from 

 their refracting power being partly equal to 

 that of the fluid surrounding them. The 

 granules may then be made visible by adding 

 water. 



FRAGILARIA, Lyngb.— A genus of Dia- 

 tomacese. 



Char. Frustules (in front view) linear, 

 symmetrical, united into straight or curved 

 flat filaments ; valves lanceolate, oblong or 

 linear; markings as in Diatoma, no no- 

 dules. 



Difl^ers from Diatoma in the filaments not 

 becoming separated into zigzag chains. 



Kiitzing enumerates sixteen species, of 

 which ten are doubtful. 



F. capucina, K. (F. rhabdosoma, E.) (PI. 

 12. fig. 33). Filaments more or less elon- 

 gate; frustules linear and rectangular in front 

 view; valves narrowly and acutely lanceo- 

 late; breadth of filament 1-700". Aquatic. 

 No striae perceptible under ordinary illumi- 

 nation. Common in pools, &c. 



F. virescens, Ralfs (F. pectinalis, Ehr.). 

 Filaments more or less elongate ; frustules 

 in front view linear, rectangular or cuneate ; 

 valves contracted and obtuse at the ends. 

 Aquatic. Endochrome green. 



One of the recognized species is marine ; 

 and several of the doubtful species are marine 

 or fossil. 



BiBL. Kiitzing, Bacill. p. 45; ibid. Sp. 

 Alg. p. 14; Ralfs, Ann. Nat. Hist. 1843, xii. 

 106. 



FREDERICELLA, Gervais.— A genus of 

 Polypi, of the order Bryozoa, and family 

 Plumatellidae. 



Char. Polypidom fixed, coriaceous, tubular, 

 branched ; polypes protruding from the ends 

 of the branches; tentacular disk orbicular; 

 tentacles about twenty-four, arranged on the 

 margin of the disk in a single series, and 

 invested at their origin by a membrane. 

 Aquatic. 



F. sultana. Polype-cells erect, cylindrical. 



Height of polypidom about 2"; tufted, 

 shrubby ; stem dichotomously branched. 



F. dilatata. Polype-cells dilated towards 

 the orifice. 



BiBL. Allman, Ann. Nat. Hist. 1844. xiii. 

 331 ; Johnston, Brit. Zoophytes, p. 405. 



FROG. — The common frog (Rana tempo- 

 raria) afi^ords a means of studying several 

 interesting points of structure. Thus, by gently 

 scraping the back of the roof of the mouth with 

 the handle of a scalpel, ciliated epithelium 

 (PI. 40. fig. 12) may be obtained, and the 

 ciliary movement studied. The circulation 

 in the web of the foot, and the phenomena 

 of inflammation may be observed, by enclo- 

 sing a frog in a wet bag, leaving one leg 

 projecting. The bag containing the frog 

 may then be placed upon a plate of wood, 

 with a circular aperture at one end, over 

 which the foot is to be extended by tying 



