FEET. 



[ 317 ] 



FERMENTATION. 



hairs. Hence a feather may be regarded 

 simply as a large, doubly or triply pinnate 

 hair. 



During development, the cell structure is 

 very distinct ; but in the mature feathers, 

 digestion with solution of caustic potash is 

 requisite to render this visible ; and fre- 

 quently even under these circumstances, the 

 nuclei alone can be detected. 



The barbs of some feathers resemble the 

 shafts, being rounded or angular, and free 

 or unattached (figs. 17 & 18) ; but in others 

 they are flattened, and linked together in a 

 remarkable manner, much resembling that 

 met with in the wings of Hymenopterous 

 and other Insects (PL 34. figs. 11 & 13), and 

 which has been so often adduced as one of 

 the many wonderful instances of design in 

 the creation. Thus the upper or outer 

 margin of each barb is fringed on both sides 

 with hair-like elongated processes or pinnae 

 (PI. 22. fig. 15 , 6), which differ in struc- 

 ture on the two sides. On one, and this 

 always the same side of each barb (fig. loft), 

 the pinnae are toothed on one edge (fig. 16 b* ), 

 whilst the pinnae arising from the other side 

 (fig. 15 c) exhibit, beyond the middle, a 

 number of curved hooks (fig. 16 a), which 

 clasp around the first kind existing upon 

 the adjacent barb, so as to retain a firm hold 

 upon them, this being aided by the teeth, 

 which prevent them from slipping. If the 

 relative position of the two sets of pinnae 

 which spring from two adjacent barbs be 

 examined, it will be seen that they cross 

 each other at a considerable angle, so that 

 any pinna from one barb crosses several of 

 those belonging to the next barb. Hence 

 each pinna is connected by its hooks with 

 several of those which it crosses ; for the 

 pinnae with hooks are situated outside or 

 above those not furnished with these ap- 

 pendages. The under or inner margin of 

 each barb is simply membranous, and curved 

 so as to overlap that of the next. 



The free barbs of feathers are often met 

 with in the examination of liquids &c. left 

 exposed to the air (figs. 17 & 18). 



BIBL. Schwann, Mik. Untersuch. ; Re- 

 clam, De Plamar. Evolut. ; Leydig. Histol. 

 99 ; R. Beck, Achr. Micr. 31. 



FEET. In descriptions, &c., of the Arti- 

 culata, especially of Insects, the word feet 

 is mostly used to designate the legs j hence 

 when met with in the w r orks of systematic 

 and other writers on these classes, it must 

 be understood to mean the legs. 



FEET OF INSECTS. See INSECTS, Legs. 



FEGATEL'LA, Raddi (Conocephalus, 

 Hill). A genus of Marchantiaceous Hepa- 

 ticae. F. conica (Marchantia cornea, Brit. 

 FL), the only British species, is not un- 

 common, and is one of the largest of the 

 tribe. It is distinguished from Marchantia 

 by its nearly entire conical fertile receptacle. 

 The dichotomously divided frond is of a 

 yellowish green colour. This genus is re- 

 markable for the mode in which the pedicel 

 of the sporange becomes detached from the 

 base of the epigone before the former bursts 

 (fig. 220) ; the perigone holds the sporange 

 firmly between its valves until empty, and 

 then lets it fall out, together with its pe- 

 dicel. Hence fully-developed sporanges 

 are seldom found in dried specimens. (See 

 MABCHANTIE^;.) 



Fig. 219. 



Fig. 220. 



Fegatella conica. 



Fig. 219. Vertical section of the upper part of a fer- 

 tile receptacle, showing four of the sporanges sur- 

 rounded by their perigones and epigones almost en- 

 closed in the conical receptacle. Magnified 10 diams. 



Fig. 220. A sporange just before bursting, enclosed in 

 its epigone ; its pedicel detached at the base. Magn. 

 20 diams. 



BIBL. Hooker, Brit. FL v. pt. 1. 107 ; Bis- 

 choff, Nova Acta, xvii. 970, pi. 68; Engl. 

 Bot. pi. 504. 



FEL'SPAR. See ROCKS. 



FEL'STONE. See ROCKS. 



FENESTRELLA, Grev. A genus of 

 Diatornaceae. 



Char. Frustules free, disciform ; disk with 

 minute radiant dots, interrupted in the 

 middle by a transverse band, composed of 

 parallel lines of dots, band terminated at 

 each end by a flat ocellus (nodule). 



F. barbadensis. Barbadoes deposit. 



BIBL. Greville, Micr. Tr. 1863, p. 67. 



FERMENTATION. Under this name 

 are understood various processes of decom- 

 position of organic compounds; although 

 it would be desirable to restrict it to those 

 taking place with the cooperation of living 

 organisms. The most familiar examples of 

 the fermentation produced by the growth 



