510 COMPARATIVE ANATOMY chap. 



abdomen behind the sexual aperture ; 2 pairs of stigmata on the 2d and 3d abdominal 

 segments) (Fig. 372, p. 529). 



Order 7. Araneid^— Spiders. 



Both cephalo-thorax and abdomen unsegmented, the latter large and egg-shaped. 

 Abdomen joined to the cephalo-thorax by a short narrow stalk, 4 to 6 pairs of 

 spinning mammilla at the end of the abdomen. ChelicerEe claw-like with poison 

 glands. Pedipalps leg-like, tei-minal j oiut in the male transformed in a peculiar manner 

 into an organ for transmitting the semen in copulation (Fig. 377, p. 535). Trachefe 

 either exclusively book-leaf, or book-leaf and tubular at the same time. 



Sub-order 1. Tetrapneumones. 



With 4 book-leaf trachefe, without tubular trachcEc. The 2 pairs of stigmata, 

 ventral, behind the base of the abdomen. Generally 4 (in Atyjius 6) spinnerets. 

 MygaU {Avicularia, Fig. 374, p. 531), Ctcniza, Aty2ms. 



Sub-order 2. Dipneumones. 



AVith 2 book-leaf tracheie whose stigmata lie at the base of the abdomen, and with 

 tubular traeheie emerging through an unpaired (less frequently paired, e.g. Dysderidce) 

 stigma behind those of the book-leaf trachese. The unpaired stigma of the tubular 

 trachefe is generally moved far back, so that it lies in front of the 6 spinnerets. 

 This sub-order includes most of the web-spinning spiders. Fam. Dysderidce (2 stig- 

 mata for the tubular trachefe) : Dysdera, Segestria. Fam. Salti grada : Salticus. 

 Attus. Fam. C itigrada (Lycosidw) : Lycosa, Tarantula. Ya,ia. Laterigrada: 3Iicrom 

 mata, Philodromui, Xysticus. Fam. Tubitelaria : Dictyna, Tegenaria, Agelena. 

 Argyroncta, Drassus, Clubiona. Fam. Ectitelaria : Linypliia, Theridmm, Pholcus. 

 Fam. Orbitelaria : Epeira, Zilla, Mda. 



Order 8. Acarina — Mites. 



Abdomen fused with cephalo-thorax. Body unsegmented. Mouth parts adapted 

 for biting, or piercing and sucking. Respiratory organs (trachefe) either present or 

 absent. Many Mites are parasitic. 



a. Mites provided with tracheae : — Fam. Trombidiido) : Troynbidimn. Fam. 

 Tcti-anychidce : Tetranyehus. Fam. Hydrachnidn: : Atax, Hydrachna, Hydrodoma. 

 The sub-families of the marine Ealacaridce: Aletes, Salacarus without trachea. 

 Fam. BdeUidcc : Bdella. Fam. Oribatida; : Oribata, Leiosoma. Fam. Gamasidce : 

 Gamasus {Vig. 361, p. 514), Uro-poda. Fam. Ixodidce: Ixodes, Argas. 



6. Mites without tracheae :— Fam. Tijroghj2jMdcs (cheese Mites) : Tyroglyphus. 

 Fam. Dermaleicliidce : Listrophorus, Analges. Fam. Sarcoptidcc : Sarcoptes. Fam. 

 Demodiddm: Demodex. Fam. PUytoptidoe : Phytoptus. 



Appendage to the Class of the Arachnoidea. 

 The Linguatulidse (Pentastoaiidse) 

 Body vermiform, generally flattened, and ringed externally. No oral appendages. 

 Two pairs of movable hooks near the mouth. "Without sensory organs, trachea, 

 Malpighian vessels, or diverticula of the mid-gilt. Male aperture in front, behind the 

 mouth ; female aperture at the posterior end of the body. Parasites, Pentastomum, 

 P. taenioides (Fig. 378, p. 537). Parasitic in the nasal and throat cavities and in 

 the cephalic sinus of the dog and wolf. The embryos, enclosed in their egg envelopes, 

 reach the exterior with the nasal mucus. If they are taken into the intestine of a 

 rabbit or a hare (or of a few other mammals) the embryos become free, pierce their 



