ACROSTICIIE.E. 



[ 13 ] 



ACTINOOOCCUS. 



Corda. It arrows in large patches on rotten 

 potatoes. Iloirmanu regards it as a mere 

 form of Trir/idflicciinn roseum, which is 

 rather a Dacfi/liian. 



BiBL. lierkeley, Cn/pfor/. Bvf. p. 294; 

 see also Trichothecium and Verticil- 



LIUM. 



ACROSTICH'E.T^..— A family of Poly- 

 podiaceous Ferns, with naked sori. 



Illustrative Genera. 



Acrostkhum. Sori seated on all the veins, 

 venules, and parenchyma, sometimes on 

 both surfaces; veins very much branched, 

 and anastomosing in more or less regidar 

 meshes. 



Flati/ceriitm. Sori forming large patches 

 on the lower surface of the fertile fronds, 

 which are dichotomously forked with stag's- 

 horu-like divisions. 



ACROS'TICI-IUM, L.— A genus of Acro- 

 sticheae(Polypodiaceous Ferns), ^^^th naked 

 sori seated on all parts of the leaf. Species 

 very numerous, mostly tropical. See 

 Hairs. 



ACTINIA. — A genus of Coelenterata 

 (Zoophytes) ; class Actinozoa. 



C/iar. Body conical or cylindrical, ad- 

 hering by a broad discoidal base ; mouth 

 simple, superior, surrounded by one or more 

 uninterrupted series of conical, undivided, 

 tubular retractile tentacula; marine. 



The species are commonly known as sea- 

 anemones, and are found on the sea-coast 

 adhering to rocks and stones. A. mesem- 

 hryayithemum (I-I5" diam.), with numerous 

 azure-blue tubercles surrounding the mar- 

 gin of its oral disk, is very common on the 

 British coast. 



The body is formed of a thick coat, the 

 inner layer'of which consists of longitudinal 

 and transverse unstriated muscular fibres. 

 The tentacles are covered with stinging 

 threads and capsules, as in the Acalephse, 

 often forming beautiful objects; and at 

 their bases are often foimd chromato- 

 phores. The space between the stomach 

 and the skin is divided into cellular 

 spaces by radiate partitions or mesen- 

 teries, the ovaries and the spermatic convo- 

 luted tubes being attached to these parti- 

 tions. 



The connective tissue of the body is com- 

 posed of numerous fibres, cells, and inter- 

 mediate stages, of extreme delicacy (PL 41. 

 fig. 1). Dispersed throughout it are nume- 

 rous spindle-shaped, flexible, organic spi- 

 cula (PI. 41. figs. 1 a and 2), many of them 



curiously marked by interrupted transverse 

 markings (lig. 2). 



In r(^productive power they almost equal 

 thellydrtT; when cut across, new tentacles 

 form in a few weeks on the lower half, and 

 each piece becomes a new animal. They are 

 usually propagated by ova ; the embryos 

 being ciliated. INIany of the species exhibit 

 the most splendid iridescent colours. 



BiBL. Johnston, Brit. Zooph.\ Tugwell, 

 Common Enfjlish Sea-Atiem. ; Gosse, Acti- 

 nol. Britnnn. 18G0, Mar. 7moI. 1, and " Be- 

 vonshire Coast ;" Bronn, Die Klass. 8fc. d. 

 Thierreichs ; Gegenbaur, Vergl. Anat. 1878 ; 

 Nicholson, Z(>o/. p. 178; Strieker, ifMjnfm 

 .y Comp. Uistol. 



ACTINIS'CUS, Ehrenberg.— A doubtfid 

 genus of Diatomacefe,provided with siliceous 

 shells bearing radiating spines. (Cohort 

 Actinisceee.) 



C/iar. Individuals microscopic, solid, ra- 

 diate, resembhng a star ; marine. 



These organisms, which are found both 

 recent and fossil, are especially remarkable 

 for their valves being frequently found per- 

 forated. Species : — 



A. Tetrasterias, Ehr. (PI. 18. fig. 1). 

 Stellate, with 4 free rays; diam. 1-1000". 

 Virginia. — A. Pentasterias, Ehr. (PI. 18. 

 fig. 2). Rays 5 ; diam. 1-1200". Recent on 

 the shores of Norway ; fossil in the chalk- 

 marl of Greece. — A. quinarius, Ehr. (PI. 

 18. fig. 3). Stellate, ravs 5, free; diam. 

 1-3000". ^gina.— ^. Sirius, Ehr. (PI. 50. 

 fig. 45). Rays 6, acute, winged at the 

 base; diam. 1-1200". Shore of Norway, 

 recent.—^. Discus, Ehr. (PL 18. fig. 4). 

 Disk-shaped, centre smooth, 8 marginal 

 ravs not exserted; diam. 1-1200". Gran. 

 — ^. Eota, Ehr. (PL 18. fig. 5). Disk- 

 shaped, centre smooth, 10 marginal rays 

 exserted; diam. 1-1900". Gran. — A.Lan- 

 ceorius, Ehr. Stellate, with 8 marginal lan- 

 ceolate rays, and some central rays which are 

 shorter on one side; diam. 1-240". Ant- 

 arctic Ocean. 



BiBL. Ehrenberg, Leb. Kreidethierchen, 

 1840, p. m-,' Monatsher. 1844, p. 76, &c. ; 

 Klitzing, Bacillarien, 1844, p. 139; Spec. 

 Algarum, 1848, p. 141. 



ACTINOB'OLUS, Stein.— A genus of 

 Infusoria. 



BiBL. Kent, Infus. 1880, p. 214. 

 ACTINGCLA'DIUM, Ehr.— A genus of 

 Mucedines (Hyphomycetous Fimgi). No 

 British species vet recorded. 



ACTINOCOC'CUS, Kiitzing.— A genus 

 of exotic Algse (marine), referred to Ri- 



