FAVUS. 



[ 257 1 



FEGATELLA. 



they form tubercles upon the branches. 

 Sometimes these tubercles open by a pore 

 on the surface, when mature, to emit the 

 spores. 



FAVUS (Porrigo in part, Willan and 

 Bateman). — A disease of the skin, charac- 

 terized by the presence of cup-shaped iso- 

 lated or aggregated crusts, consisting of a 

 Fungus. (See Achorion and Puccinia.) 



FEATHERS, of Birds. — Feathers agree 

 in all essential points of structure with the 

 hairs of other animals. 



Each feather is composed of a quill, con- 

 taining the pith, a shaft, and a vane or beard, 

 with its barbs. The whole consists of a 

 number of epidermic cells, often containing 

 pigment, but in most ])arts so consolidated 

 or fused together as to be imperceptible. 



In the quill, the cells are flattened, elon- 

 gated, and arranged with their long axis in 

 the direction of that of the feather, and their 

 nuclei have the same form as those of the 

 corresponding part (cortex) of the human 

 hair. The cells of the pith are often undis- 

 tinguishable in old feathers, whilst in the 

 younger ones they are very distinct, rounded 

 or polygonal, and contain air. The shaft 

 and the barbs exhibit the same cortical and 

 medullary structure ; the latter is often beau- 

 tifully distinct (PI. 17. figs. 14 & 15 c), and 

 causes them to resemble closely the hairs of 

 some Rodents. The barbs are sometimes 

 furnished with secondary barbs, or processes, 

 resembling them in form, but differing mostly 

 in the absence of the pith. 



Feathers are developed in a capsule, and 

 from a pulp or matrix, as in the case of 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 frequently 

 even under these cncumstances, the nuclei 

 alone can be detected. 



The barbs of some feathers resemble the 

 shafts, being romided or angular, and free or 

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

 they are flattened, and linked together in a re- 

 markable manner, much resembling that met 

 with in the wings of Hvmenopterous andother 

 Insects (PI. 27. figs, i I & 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 pinnaj (PI. 17. fig. 15 

 a,b), which diff^er in structure on the two 



sides. On one, and this always the same 

 side of each barb (fig. 15 b), 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 consider- 

 able 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 situ- 

 ated outside or above those not furnished 

 with these appendages. 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, Mlkrosk. Untersuch. ; 

 Reclam, De Plumar. Evolut. Sf-c. 



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

 culata, especially of Insects, the word feet is 

 mostly used to designate the legs; hence 

 when met with in the works of systematic 

 and other writers on these classes, it must 

 be understood to mean the legs. 



FEET, OF Insects. See Insects, Legs. 



FEGATELLA, Raddi ( ConocephalusJliU). 

 — A genus of Marchantiaceous Hepaticaceae. 

 F. conica {Marchantia conica, Br. Flora), the 

 only British species, is not uncommon, and 



Fig. 223. 



Fig. 224. 



Fegatella conica. 



Fig. 223. Vertical section of the upper part of a fertile 

 receptacle, showing four of the sporanges surrounded by 

 their perigones and epigones almost enclosed in the coni- 

 cal receptacle. iMagnified 10 diams. 



Fig. 224. A sporange just before bursting, enclosed in 

 its epigone ; its pedicel detached at the base. Magn. 20 

 diaras. 



is one of the largest of the tribe. It is dis- 

 tinguished from Marchantia by its nearly 



s 



