Spiders and Their Near Relatives 



sternite shows indications of being composed of two sternites, 

 which would bring the total number of sternites up to nine, thus 

 equalling the tergites in number." (Pocock '02.) 



The various forms of the labium, the sternum, and the 

 sternites of the first two abdominal segments afford characters 

 for limiting the larger divisions of the order. 



The eyes are only two in number in our species and are sit- 

 uated on a prominent tubercle, like a lookout tower, near the 

 middle of the cephalothorax, an eye looking out on each side. 



Near the anterior margin of the cephalothorax, on each side 

 opposite the attachment of the first pair of legs, there is a small 

 opening; these are sometimes called the lateral pores and some- 

 times' the openings of Krobn's glands. They are the openings 

 of scent glands which have been described by Krohn ('67) and by 

 Rossler ('82). 



The respiratory organs are tubular tracheae, which open by 

 a pair of spiracles situated on the ventral side at the juncture of 

 the lateral margins of the cephalo- 

 thorax and the second abdominal ster- 

 nite. Secondary spiracles have been 

 found on the legs of some members of 

 this order by Hansen (See Loman '96). 



The reproductive organs open on 



., , , ,. . , , Fig. so. CADDO AGn.IS WITH 



the boundary between the cephalo- the ovipositor exposed 

 thorax and the abdomen on the 



middle line of the ventral aspect of the body; the opening is 

 covered by a prolongation of the sternite of the first abdominal 

 segment, which is called for this reason the genital sternite. 

 The female is provided with a large ovipositor, and the male 

 with a large penis; each of these structures is usually retracted 

 within a sac. The form of these organs varies in differenl 

 species and has been used by systematists for distinguishing 

 species. It is well therefore to' preserve specimens with these 

 organs exposed (Fig. 50). This is "a simple operation, requir- 

 ing only that the abdomen of the living specimen be compressed 

 between the thumb and finger, when these organs will be extruded. 

 and if the specimen is immediately chopped into alcohol will or- 

 dinarily remain exposed" (Weed '89a). As the first abdominal 

 sternum is thrust far forward the opening of the reproductive 

 organs in some tonus is not far removed from the mouth. 



55 



