DEMATIUM. 



[ 240 ] 



DEMODEX. 



thickened at the articulations j spores 

 irregularly biconical, somewhat angular, 

 attached in whorls. 



Sporodum. Filaments erect, jointed ; 

 threads of inarticulate spores moniliform, 

 seated towards their base. 



Allied or uncertain Genera. 



Blastotrichum. Pedicels ascending or 

 floating, very much branched, continuous ; 

 spores oblong, transversely septate. 



Stachyobotrys. Pedicels branched, sep- 

 tate ; branches crowded at the tips with 

 whorls of Hiainniillary very short branchlets 

 forming a capitulum ; spores didymous. 



Helicotrichum. Filaments creeping, 

 branched, septate only at the tips j spores 

 spirally curled, somewhat septate. 



DEMA'TIUM, Pers. A genus of Dema- 

 tiei (Hyphomycetous Fungi), growing upon 



Fig. 162. Fig. 163. Fig. 164. 



Dematium griseum. Magnified 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. griseum, Pers. (figs. 162-4). On 

 rotten hazel-stumps. Cheetopsis Wauchii, 

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



BOTRYUM. 



BIBL. Berk. Hook. Brit. Fl. v. pt. 2, 338 ; 

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

 Sum. Veg. 499 j Corda, Ic. Fung. i. pi. 4. 

 figs. 242, 243. 



DEMO'DEX, Owen (Simonia, Gerv.). 

 A genus of Arachnida, the exact systematic 

 position of which is doubtful, "although 

 usually placed in the family Acarina. 



Char. Legs terminated by two claws 

 (only one, Beck), no acetabula; abdomen 

 annulose. 



D.foUiculorum (PI. 6. fig. 42), the Aca- 

 rus, Simonia, or Entozoon foUicidorum of 

 some authors, inhabits the 'sebaceous and 



hair-follicles of the human skin. The mi- 

 nute size of the various parts renders it ex- 

 tremely difficult to isolate them. It varies 

 in length from about 1-150 to 1-50". 



At the anterior part of the body are two 

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

 joint longest, 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 6), the mandibles. Behind 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 striae. 



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 follicles existing 

 upon the sides and alae of the nose, especially 

 when 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 gentle heat. Or the secretion 

 may be digested in a mixture of alcohol and 

 ether, to dissolve the fatty matter, and then 

 treated with solution of potash. 



The secretion contains the ova, the young 

 animals, and the exuviae. When contained 

 in the follicles, the tail is directed towards 

 their orifice. 



Var. caninus occurs in the pustules of the 

 skin of the dog affected with the " mange." 

 The average size of this is less than that of 

 D.foUiculorum, amountingto 1-150 to 1-100" 

 in length. It does not appear to constitute 

 a distinct species ; for Gruby found that, 

 by inoculating the dog with the human 

 parasite, a disease resembling, if not identi- 

 cal with, the mange was produced. 



Var. cati, on the cat ; about less than 

 D.foUiculorum. 



BIBL. Simon, Mutter's Archiv, 1842,218; 

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

 enaer's Apteres, iii. 282 ; Wilson, Tr. Hoy. 

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

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



