DEMATIUM. 



[ 240 ] 



DEMODEX. 



thiclieiied at the articulatious ; spores 

 irreg-iilarly bicouical, somewhat ai)gular, 

 attached in whorls. 



Sporodum. Filaments erect, jointed; 

 threads of inarticulate spores moniliform, 

 seated towards their base. 



Allied or uncertain Oenera. 



Blasfotrichmn. Pedicels ascending or 

 floating, very much branched, continuous ; 

 spore.s oblong, transversely sei)tate. 



Stachyohotrys. Pedicels branched, &&\\- 

 tate ; branches crowded at the tips with 

 whorls of niammillary very sliort branchlets 

 formiug a capitulum ; spores didymous. 



Helicotrichum. Filaments creeping, 

 branched, septate only at the tips ; spores 

 spiraliv curled, somewhat septate. 



DEMA'TIUM, Pers.— A genus of Dema- 

 tiei (Hyphomycetous Fungi), groAving upon 



Fig. 162. 



Fig. 163. 



Fig. 164. 



Dematium griseum. Magniiled 200 diameters. 



dry leaves, bark, &c., distinguished by the 

 sporiferous branchlets arising closely toge- 

 ther near the base of the erect filaments. 

 British species : 



D. yrisemn, Pers. (figs. 162-4). On 

 rotten hazel-stumps. C/xstopsis Wauchii, 

 Grev. Sc. Crypt Fl. pi. 236. See Echino- 



BOTRYUM. 



BiBL. Berk. Hooh. Brit. Fl. v. pt. 2, 338 ; 

 Ann. N. H. i. 260, vi. 435; Grev. /. c. ; Fries, 

 Sum. Vc(/. 499 ; Corda, Ic. Fung. i. pi. 4. 

 figs. 242,' 243. 



DEMO'DEX, Owen (Simonia, Gerv.).— 

 A genus of Arachnida, the exact systematic 

 position of Avliich is doubtful, although 

 usually placed in the fixmily Acarina. 



Chcu: Legs terminated by two claws 

 (only one, Beck), no acetabula ; abdomen 

 annidose. 



D.folUcHhntm (PI. 6. fig. 42), the Ava- 

 rus, Simouia, or Entozoon foUiculormn of 

 some authors, inhabits the sebaceous and 



hair-follicles of the human skin. The mi- 

 nute size of the various parts renders it ex- 

 tremelv difficult to isolate them. It varies 

 in leng-th from about 1-150 to 1-50". 



At the anterior part of the body are two 

 two-jointed organs (PI. 6. fig. 43rt), the basa 

 joint longe.st, the distal smallest, and ter- 

 minated by a strong claw ; these appear 

 to represent maxillary palpi. Between 

 these are two narrow elongated organs (fig. 

 43. i), the mandibles. Behmd these is a 

 triangular labrum (fig. 43 c) ; a labium has 

 also been described. 



Above or upon the basal joint of the palpi 

 are two minute tubercles, one on each side 

 (fig. 43 d). Similar tubercles are seen upon 

 the dorsal surface of the thorax, between 

 the second and third, and the third and 

 fourth pairs of legs. 



On each side of the thorax are four pairs 

 of very short conical legs ; these are appa- 

 rently three-jointed, and marked by irregular 

 fine transverse stria). 



The abdomen is longer than the thorax, 

 tapers posteriorly, and exhibits indications 

 of transverse rings, in the form of numerous 

 delicate transverse lines. 



These animals may be obtained by press- 

 ing out the contents of the folhcles existing 

 upon the sides and alte of the nose, especially 

 Avhen these appear enlarged, whitish, and 

 exhibit a terminal black spot. A drop of oil 

 should then be added to the secretion, and 

 the whole allowed to macerate for some 

 hours at a gen'tle heat. Or the secretion 

 may be digested in a mixture of alcohol and 

 ether, to dissolve the fatty matter, and then 

 treated with soluticm of potash. 



The secretion contains the ova, the young 

 animals, and the exuvia^. When contained 

 in the follicles, the tail is directed towards 

 their orifice. 



Var. caninus occurs iu the pustules of the 

 skin of the dog afl'ected with the " mange." 

 The average size of this is less than that of 

 D.follicnlormn, amomitingto 1-150 to 1-lUO" 

 iu length. It does not appear to constitute 

 a distinct species ; for Gruby found that, 

 by inoculating the dog with the human 

 parasite, a disease resembUng, if not identi- 

 cal Avith, the mange was produced. 



Var. cati, on the cat : about \ less than 

 I), follicidorum. 



BiBL. Simon, 3Iidler'sArckiv, 1842, 218: 

 Owen, Hunt. Led. i. 251; .Gervais, Walck- 

 enai}r\^ Apthres, iii. 282 ; Wilson, Tr. Hoy. 

 Soc. 1844, 305; Tidk, Ann. N. H. 1844, 

 xiii. 75 ; Gruby, Ed. Mn. Jn. vii. 333 ; 



