ARECA. 



ARROW-ROOT. 



eapillitium ochraceous, capillitium erect ; 

 peridium ovate. 



6. A. ochroleuca, Fr. Spores and capil- 

 litium pale-ochraceous, peridium globose, 

 evanescent ; smaller than the preceding ; 

 1-12" high. 



ARECA, L. A genus of flowering plants 

 (Fam. Palmaceae). The albumen of the seed 

 of the Areca catechu, the Areca nut as it is 

 called, affords a good instance of horny con- 

 sistence produced by secondary layers upon 

 the cell-walls (PI. 38. figs. 21 & 22). See 

 ALBUMEN (of seeds). 



AREGMA, Fries. See PHRAGMIDIUM. 



AREOLAR TISSUE of animals. See 

 CELLULAR TISSUE. 



ARGAS, Walck. A genus of Arachnida, 

 of the order Acarina and family Gamasea. 



Char. Rostrum inferior, concealed, as 

 also the palpi, beneath a projection of the 

 anterior part of the body; under part of 

 body granular, not scaly, and consisting of a 

 single piece ; first joint of the palpi longest ; 

 legs approximate at their insertion, feet 

 terminated by two claws, but no vesicle. 



These animals are frequently parasitic upon 

 pigeons, fowls, &c. ; some live in gardens. 



A. reflexus (Rhynchoprion Columbce, 

 Herm.). Body marked with tortuous fur- 

 rows and depressions, yellowish or violet after 

 food. On pigeons, especially when young. 



A. persicus. Blood-red colour, back co- 

 vered with scattered elevated white spots. 

 The venomous bug of Persia ; said to cause 

 death in the human subject. 



There are other species. 



BIBL. Walcken., Apteres, iii. (Gervais). 



ARGULU S,Mull.-A genus of Crustacea, of 

 the order Siphonostoma and family Argulidse. 



Char. Carapace membranous, covering 

 the cephalothorax like a shield; antennae 

 four, short, concealed beneath the carapace ; 

 anterior two-jointed, terminal joint hooked, 

 posterior four-jointed ; rostrum acuminate ; 

 five pairs of legs, the place of the first (6th) 

 pair being occupied by two suckers ; second 

 pair short, five-jointed, the two basal joints 

 spinous, the last joint with two small hooks ; 

 the last four pairs of legs two-cleft, and fur- 

 nished w r ith ciliated filiform processes. 



A.foliaceus (PL 15. fig. 1). Parasitic on 

 the stickle-back (Gasterosteus) and other 

 fishes ; carapace greenish. 



BIBL. V. d. Hoeven, Handb. d. Zool. ; 

 Baird, Brit. Entomostraca. 



ARPACTICUS, Baird. A genus of Ento- 

 mostraca, of the order Copepoda and family 

 Cyclopidae. 



Char. Head undistinguishable from thorax; 

 foot-jaws two pairs, forming strong cheliform 

 hands; antennae in male furnished with a 

 swollen hinge-like joint; antennules (infe- 

 rior antennae) simple; legs five pairs, the 

 fifth pair rudimentary ; eye single ; ovary 

 single. 2 species : 



A. chelifer and A. nobilis. Marine, closely 

 resembling Cyclops. 



BIBL. Baird, Brit. Entom. 



ARRENURUS,Duges. A geuusof Arach- 

 nida, of the order Acarina and family 

 Hydrachnea. 



It contains those species in which the 

 posterior part of the body of the male is 

 narrowed and produced into a truncate or 

 cylindrical appendage. The body of the 

 female is truncated posteriorly. The prolon- 

 gation is terminated by two angles and a 

 sinuous intervening margin. At the middle 

 of the latter is situated the penis; above 

 which are two hooks. In both sexes the 

 back is hard, crustaceous, as if shagreened, 

 or spinous. In some species the thicker 

 layer of the skin is furnished with a number 

 of conical apertures (PI. 2. fig. 12). The 

 eyes are two, distant, blackish. The intes- 

 tinal caeca are distinguishable through the 

 skin. The mouth is round and surrounded 

 by a kind of hood (PL 2. fig. 13 e). 



Arrenurus viridis, Duges' typical species 

 (PL 2. fig. 13), has the palpi short and clavate 

 (a) ; the fourth joint longest and largest, the 

 fifthfalcate and the mandiblesunguiculate (b). 



The species are very numerous and of almost 

 all colours, red, green, yellow, grey, purple. 



BIBL. Walcken. Apteres, iii. ; Duges, 

 Ann. d. Sc. nat., 2 ser. i. ; Koch, Ueber- 

 sicht des Arachnidensystems. 



ARROW-ROOT. A name given to va- 

 rious kinds of starch, derived from the plant 

 Mar ant a arundinacea, and other species. 

 True West India arrow root is from this 

 (PL 36. fig. 18) and M. Allonga and M. 

 nobilis (N. O. Marantaceae). East India 

 arrow-root is obtained from species of Cur- 

 cuma (N. O. Zingiberaceae) (PL 36. fig. 19), 

 but Maranta arundinacea is also grown 

 there, as its fecula is brought from Singa- 

 pore. Tahitan arrow-root (PL 36. fig. 22) 

 is obtained from the plant called Tacca pin- 

 natifida (N. O. Taccaceae), and the substance 

 called Portland arrow-root (PL 36. fig. 11), 

 is extracted from the Arum maculatum 

 (N. O. Araceae), a common hedge-weed in 

 this country. In all these cases the fecula 

 consists of starch- grains, which are produced 

 in great quantity before the season of rest, in 



