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. Araneidse 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 mammillae at the end of the abdomen. Chelicera claw-like with poison 

 glands. Pedipalps leg-like, terminal joint in the male transformed in a peculiar manner 

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

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



Sub-order 1. Tetrapneumones. 



With 4 book-leaf trachea, without tubular tracheae. The 2 pairs of stigmata, 

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

 Myijale (Avicularia, Fig. 374, p. 531), Cteniza, Atypus. 



Sub-order 2. Dipneumones. 



With 2 book-leaf trachea whose stigmata lie at the base of the abdomen, and with 

 tubular tracheae emerging through an iinpaired (less frequently paired, e.g. Dysderidce) 

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

 tracheae 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 trachea) : Dysdera, Segestria. Fam. Salti grada : SaUicus, 

 Attus. Fam. Citigrada (Lycosidce) : Lycosa, Tarantula. Fam. Laterigrada: Microm- 

 mata, Philodromus, Xysticus. Fam. Tubitelaria : Didyna, Tegenaria, Agelena, 

 Argyroncta, Drassus, Clubiona. Fam. Ectitelaria : Linyphla, Thcridium, Pholcus. 

 Fam. Orbitclaria : Epeira, Zilla, Mcta. 



Order 8. Acarina Mites. 



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

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

 absent. Many Mites are parasitic. 



a. Mites provided with tracheae: Fam. Trombidiidcc : Trombidium. Fam. 

 Tetranychidcc : Tctranyclius. Fam. Hydrachnidfe : Atax, Hydrachna, Hydrodoma. 

 The sub-families of the marine Halacaridce : Aletes, Halacarus without trachea. 

 Fam. Bdellidcc : Bdclla. Fam. Oribatidce : Oribata, Lciosoma. Fani. Gamasidce : 

 Gamasus (Fig. 361, p. 514), Uropoda. Fam. Ixodidcc: Ixodes, Argas. 



b. Mites without tracheae : Fam. Tyroglypliidcc (cheese Mites) : Tyroglyphus. 

 Fam. Dcrmaleichidce : Lislrophorus, Analges. Fam. Sarco2}tidcc : Sarcoptes. Fam. 

 Dcmodieidcc : Demodex. Fam. Pliytoptidcc : Phytoptus. 



Appendage to the Class of the Arachnoidea. 

 The Linguatulidae (Pentastomidae) 



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-gut. Male aperture in front, behind the 

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

 P. taenioidcs (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 



