ACROSTALAGMUS. 



[ 11 ] 



ACTINOCOCCUS. 



branched, and anastomosing in more or less 

 regular meshes, with free venules. 



iii. PoLYBOTRYA. Sori on all the veins, 

 venules and the parenchyma ; veins pinnate, 

 scarcelv anastomosing. 



ACROSTALAGMUS, 

 Corda. — A genus of Mu- 

 corini (Physom^cetous 

 Fungi), of great beauty. 

 No British species as yet 

 recorded (?). The accom- 

 panying fi gure represents 

 a continental species, A. 

 parasitans (fig. 2), occur- 

 ring upon Cephalospo- 

 rium Acremonium. The 

 globular heads at the ex- 

 tremities of the branches 

 are vesicles or peridia, 

 like those of Aspergillus. 

 The end of the branch 

 projects into the interior 



and produces spores Acrostalagmus parasitans 



which become detached (iiighiy magnified). 

 in the peridium ; this finally vanishes, and 

 the verj^ minute spores are set free. A. cin- 

 nabarinus grows in large patches on rotten 

 potatoes: spores 1-5000". 



ACROSTICHUM, L.— A genus of Acro- 

 stichese (Polypodaeous Ferns), with naked 

 sori seated on all parts of the leaf. See 

 Hairs. 



ACTINIA.— A genus of Poh^ies (Zoo- 

 phytes). 



Char. Body conical or cylincbical, ad- 

 hering by a broad discoidal base ; mouth 

 simple, superior, surrounded by one or more 

 uninterrupted series of conical, undivided, 

 tubular tentacula, which are entirely retrac- 

 tile; marine. 



Dr. Johnston describes 20 British species. 

 They are commonly known as sea-anemones, 

 and are found on the sea-coast adhering to 

 rocks and stones. A. mesemhryanthemum 

 (I-H in. diam., with numerous azure-blue 

 tubercles surrounding the margin of its oral 

 disc) 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 muscular fibres. The tenta- 

 cles are hollow. The space between the sto- 

 mach and the skin is divided into cellular 

 spaces by perpendicular partitions ; the ova- 

 ries are situated in these spaces, and the 

 spermatic convoluted tubes lie beneath the 

 partitions. 



The fibro-areolar tissue, of which the 

 parenchyma of the body consists, is com- 



posed of numerous fibres, cells, and interme- 

 diate stages, of extreme delicacy (PI. 33. 

 fig. 1), and somewhat resembUng the fibro- 

 plastic tissue met with abnormally in the 

 human body. Dispersed throughout it are 

 numerous s]iindle-shaped, flexible, organic 

 spicula (PL 33. figs. 1 a and 2), many of 

 them curiously marked by interrupted trans- 

 verse markings (fig. 2). 



In reproductive power they almost equal 

 the Hydrse ; 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, which pass from 

 the ovaries into the stomach, where they are 

 developed. The young have fewer tentacles 

 than the adults. Many of the species exhi- 

 bit the most splendid iridescent coloui^s. 



BiBL. Johnston, Hist, of British Zoo- 

 phytes, 1847. 



ACTINISCUS, Ehrenberg.— A genus of 

 Diatomaceae, provided t\'ith sihceous shells 

 bearing radiating spines. 



Char. Individuals microscopic, solid, ra- 

 diate, resembling a star ; marine. 



These organisms, which are found both 

 recent and fossil, are ill understood at pre- 

 sent. They are especially remarkable for 

 their valves being frequently found perfo- 

 rated. Species : — 



1 . A. Tetrasterias, Ehr. Stellate, with 4 

 free rays ; diam. I-IOOO". Virginia. 



2. A. Pentasterias, Ehr. Rays 5 ; diam. 

 1-1200". Recent on the shore of Norway; 

 fossil in the chalk-marl of Greece. 



3. A. quinarius, Ehr. Stellate, rays 5, 

 free; diam. 1-3000". ^Egina. 



4. A. Sirius, Ehr. Rays 6, acute, winged 

 at the base ; diam. 1-1200". Shore of Nor- 

 way, recent. 



5. A. Discus, Ehr. Disc-shaped, centre 

 smooth, 8 marginal rings not exserted ; diam. 

 1-2000". Oran. 



6. A. Rota, Ehr. Disc-shaped, centre 

 smooth, 10 marginal ravs exserted; diam. 

 1-1900". Oran. 



7- A. Lancearius, ^hr. Body stellate, with 

 8 marginal lanceolate rays, and some central 

 shorter, enlarged at one side, single, deci- 

 duous; diam. 1-240". Antarctic Ocean. 



BiBL. Ehrenberg, Leb. Kreidethierchen, 

 1840, p. 69; Monatsbericht, 1844,p. 76, &c.; 

 Kutzmg,Kieselschal.Bacillarien,\S44,Y>.\S9; 

 Species Al(/ arum, 1849, p. 141. 



ACTINOCLADIUM, Ehr.— A genus of 

 Mucorini (Physomycetous Fungi). No 

 British species vet recorded. 



ACTINOCOCCUS, Kutzing.— A genus 



