AEACHXIDA. 



[ 68 ] 



AEACIJKEDA. 



tiiVx^p, the reinaiuder being covered with 

 hairs. Each spinning-tube consists of two 

 parts : — a thicker basal portion ; and a thin 

 terminal portion, from the orifice of which 

 the substance of the fibre exudes (PI. 6. fig. 

 10, 10 «, separate tubes). The number of 

 these spinning-tubes vai'ies according to the 

 species, the sex, and the age of the spiders. 

 In some there are more than 1000, in others 

 400, 300, 100, &c., and in others still fewer. 

 The glands which secrete the tenacious 

 transparent secretion are very variable in 

 number, fiirm, and arrangement, and occupy 

 the interstices of the other abdominal ■vis- 

 cera, consist of sacs and tubes, lined with nu- 

 cleated cells, and either simple or variously 

 ramified, terminating in ducts which open 

 at the roots of the spinning-tubes. 



The filaments of which the webs of many 

 spiders are composed are not all alike. The 

 radiating filaments are but little elastic, and 

 are composed simply of one or more threads; 

 whilst the more numerous (tangential) fila- 

 ments connecting these are covered at tole- 

 rably regular intervals with minute spherical 

 masses of glutinous matter (PI. 6. fig. 11), 

 the filaments themselves being highly elas- 

 tic. These masses give the fibres an elegant 

 beaded appearance under low powers of the 

 microscope. The viscid masses cause the 

 more ready adhesion of the filaments to in- 

 sects which may accidentally become en- 

 tangled in them, and render the spider more 

 sure of holding liis prey. 



Propagation. — The Araclmida generally 

 are propagated by sexes. The sexual appara- 

 tus consists of two ovarian or seminal sacs, 

 sometimes fused together in the middle line ; 

 they are situated in the abdomen, and termi- 

 nate in two excretory ducts, which usually 

 open at a common orifice placed at the base 

 of the abdomen, or below the cephalothorax. 

 A penis is not generally present ; theseminal 

 fluid is applied to the vulva of the female 

 by the maxillary palpi of the male. 

 Parthenogenesis has been observed in 

 Acarina. 



Spiders are oviparous : the eggs are en- 

 veloped in a cocoon, and are often elegantly 

 sculptured. 



There is no metamorphosis, but repeated 

 erdysis. 



The Arachnida may be thus subdivided : — 

 Order 1. Arankida. Cephalothorax con- 

 stricted from the unj oiuted abdomen ; 

 palpi unarmed. 

 Order 2. PEDiPALn (Phrynida). Cepha- 

 lothorax distinct from the jointed abdo- 



men ; palpi large, leg-like, chelate at the 

 end. (Pulmonary sacs present.) 

 Order 3. SoLiFrG.i (Solpugida). Cepha- 

 lothorax distinct from the jointed abdo- 

 men ; palpi fihfurm, extended, as long as 

 the legs, unarmed. 

 Order 4. Pseudoscorpioxes (Obisida) ; 

 Book-scorpions. Cephalothorax distinct 

 from the ringed abdomen ; palpi large, 

 chelate. (Tracheae only present.) 

 Order 5. Phalangita (Opilionina) ; Har- 

 vest-spiders. Cephalothorax distinct from 

 the annulate or transversely plicate abdo- 

 men ; palpi simple, filiform ; mandibles 

 chelate ; legs very long, terminated b}' a 

 single claAv. 

 Order 6. Acarina (Mites). Head, thorax, 

 and abdomen fused together; legs di- 

 stinctly jointed ; palpi simple. 



Fam. 1. Acarea. Head terminated in 

 front by an eraarginate labrum, or single 

 bifid process ; palpi adnate or adherent to 

 the labium, difficultly distinguished ; 

 mandibles chelate ; no distinct ocelli ; 

 legs generally terminated by a vesicle or 

 adhesive acetabulum and claAvs. 



Fam. 2. Oribatea (Beetle-mites). Body 

 covered by a hard horny envelope ; man- 

 dibles chelate ; palpi fusiform, 6-joiuted; 

 legs furnished with claws, but no vesicle 

 or acetabulum. 



Most of the species live in mosses at 

 the roots of trees ; in some the body is sur- 

 rounded bya projectinglamella on each side. 



Fam. 3. Ixodea (Ticks). Palpi canali- 

 culate, sheathing the rostrum ; mandibles 

 tluee-jointed, basal joint internal, second 

 joint external and long, third short and 

 denticulate ; labium covered with reflexed 

 teeth. (Parasitic.) 



Fami. 4. Gamasea (Insect-mites). 

 Palpi free, filiform ; mandibles chelate ; 

 feet with two claws ajid a carimcle, or a 

 lobed membranous appendage; ocelli none 

 or indistinct. (Generally parasitic.) 



Fam. 5.' Ilydrachnea (Water-mites). 

 Palpi with the last joint unguiculate or 

 spinous ; two or four distinct ocelli ; coxjb 

 broad, legs generally ciliated, natatory, 

 the posterior longest. (Aquatic.) 



Fam.d Bdellea (Snouted mites). Palpi 

 antenniform ; mandibles terminating in 

 claws or pincers ; rostrum resembling an 

 elongated head ; body generally divided 

 between the second and third pairs of legs 

 by a transA^erse fiu-row or stricture. 



The species are minute, more or less 

 soft, variously coloured, and living in 

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