AEROW-KOOT. 



C 73 ] 



ARTERIES. 



culate (6). According to Murray, this is the 

 male of Atax histrionicus ! 



The species are very numerous and of almost 



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



BIBL. Walcken. Apteres, iii.; Duges, Ann. 



d. Sc. N. 2 ser. i. j Koch, Uebersicht $c. ; 



Murray, JSc. Ent. p. 154. 



ARROW-ROOT. A name given to va- 

 rious kinds of starch, derived from the plant 

 Maranta arundinacea and other species. 

 True West-India arrow-root is from this 

 (PL 46. fig. 26) and M. allonga and M. no- 

 bilis (N. 0. Marantaceae). East-India arrow- 

 root is obtained from species of Curcuma 

 (N. O. Zingiberacese) (PI. 46. fig. 19), and 

 apparently also from a Sagus, if we may judge 

 from a specimen (PI. 46. fig. 18) from Singa- 

 pore. Tahitan arrow-root (PI. 46. fig. 22) is 

 obtained from the plant called Tacca pinna- 

 tifida (N. 0. Taccaceae) ; and the substance 

 called Portland arrow-root (PL 46. fig. 1 1) 

 is extracted from the Arum maculatum (N. 

 O. Araceae), a common hedge-weed in this 

 country. In all these cases the fecula con- 

 sists of starch-grains, which are produced in 

 great quantity before the season of rest, in 

 the succulent tubers or rhizomes of the 

 plants; the arrow-root is extracted from the 

 grated root-stalks by washing, to separate 

 the cellular tissue and remove the often 

 acrid juices. See STARCH. 



The arrow-root of the shops is subject to 

 adulteration with cheaper kinds of starch, 

 especially with sago and potato-starch. 



BIBL. Pereira, Mat. Med. ; Hassall, Food 

 and its Adulterations, p. 31. 



ARSENIC. The common term for arse- 

 nious acid. Arsenious acid assumes two 

 crystalline forms, and occurs also in an 

 amorphous state. 



The most common form is the octahedral 

 or tetrahedral. The second (right rhombic) 

 is less common, and is only obtained by 

 sublimation. Attention to the form of the 

 crystals is important, because it is used as 

 a means of identifying arsenic in cases of 

 poisoning. It must, however, be borne in 

 mind that protoxide of antimony (Sb 3 ) 

 yields crystals by sublimation of exactly 

 the same form as those of arsenious acid 

 (PL 10. fig. 22). 



Solution of arsenious acid is sometimes 

 used as a preservative liquid for animal 

 preparations. 



BIBL. Guy, Mic. Tr. 1861, p. 54. 

 ARTE'MEA, Leach. A genus of Ento- 

 mostraca, of the order Phyllopoda and fa- 

 mily Branchiopoda. 



Char. Abdomen prolonged in the form of a 

 tail, composed of nine segments or joints, the 

 end joint simply divided into two lobes ; 

 superior antennae slender and filiform in both 

 sexes ; inferior antennae in the male large, 

 flat, curved downwards and two-jointed, re- 

 sembling horns; in the female short, pointed 

 and slightly curved; basal joint of male 

 inferior antennas provided with a short coni- 

 cal process. 



A. salina. The Lymington shrimp or 

 brine-worm. Found in the salt-pans at 

 Lymington. Length about 1-2". 



Each segment of the thorax shortly bi- 

 lobed at the apex, and with a pair of bran- 

 chial feet; each lobe of the end joint of abdo- 

 men giving off several short setae. Agrees 

 generally in structure with Branchipus. 



BIBL. Baird, Brit. Entom.; Rackett, 

 Linn. Tr. xi. 



ARTERIES. These are the tubes or 

 vessels which convey the blood from the 

 heart to the various parts of the body. The 

 structure of the arteries is very complicated 

 and difficult of investigation ; and the coats 

 or tunics of which they consist are so inti- 

 mately connected as to be by no means 

 easily separable. 



In the larger arteries, three coats are 

 usually distinguishable, an outer or adven- 

 titious coat, a middle, and an inner coat or 

 intima, with its epithelial lining. Their 

 composition and thickness vary in arteries 

 of different sizes. 



The general character of the arteries is 

 that the middle coat is thick and strong, 

 consisting of several layers, and its elements 

 run transversely. In the largest arteries it 

 is yellow, very elastic and of great strength ; 

 as the vessels become smaller, it diminishes 

 in thickness, becoming redder and more 

 contractile ; and near the capillaries it is very 

 thin, finally disappearing. The inner coat 

 is always thin, yet thickest in the large ves- 

 sels ; whilst the outer coat is absolutely 

 thinner in these than in those of a moderate 

 size, in which it equals or even exceeds the 

 middle coat. 



In the small arteries the epithelial lining 

 consists of very delicate pale, flattened, fusi- 

 form cells with longish oval nuclei. 



An elastic layer is expanded beneath the 

 epithelial layer, which is smooth in the 

 living vessels, whilst in these, when empty, 

 it exhibits numerous transverse or longitu- 

 dinal folds. It form s what is called a fenes- 

 trated membrane, generally exhibiting more 

 or less distinct reticulated fibres, and usually 



