153 



Order ARANE^E. 



Integument usually covered with a protective layer of simple or 

 feathery (plumose), rarely scale-like (st/uainiform) hairs, interspersed 

 with long erect tactile bristles or setae. Short arid thick bristles 

 form spines or spinules. A mat of close-set hairs of uniform length 

 is termed a pad or scopula, and the bunch of hairs that frequently 

 projects on each side of the claws is called the ungual tuft. On 

 the protarsus of the 4th leg there is frequently a single or double 

 row of short hairs, forming an organ called thecalamistrum, which 

 always accompanies the cribellum (p. 154). In some cases there is 

 a cluster of spines (rastellum) overhanging the base of the fang on 

 the mandible, and in connection with the jaws there are sometimes 

 .spines or bristles variously modified to form stridulating-organs. 



The carapace is marked with a groove or pit, the thoracic fovea, 

 from which shallow grooves usually radiate to the margins, the 

 anterior pair defining the head-region. The eyes, normally 8 in 

 number, are typically arranged in an anterior and posterior row, 

 and are termed anterior median, posterior median, anterior lateral, 

 and posterior lateral on each side. The eye-line, or line passing 

 through the centres of the four eyes of a row, may be straight, 

 procurved (i. e., curved with the convexity backwards), or recurved 

 (i. e., curved with the convexity forwards). The four median eyes 

 are termed the ocular quadrangle. The area, if any, between the 

 anterior row of eyes and the edge of the carapace is called the 

 .clypeus. 



The mandibles consist of two segments, the basal containing a 

 poison-gland ; the apical or fang is spiniform and closes against 

 the lower side of the basal segment, fitting into a groove, the 

 fang-groove, which is often toothed. The palpi resemble dwarfed 

 limbs, and consist of six segments, named coxa, trochanter, femur, 

 patella, tibia, tarsus. The coxa is usually furnished with a large 

 process or maxilla, which projects forwards on each side of the 

 labium. The tarsus is unmodified in the female. In the male it 

 is modified to subserve copulation, and is furnished with an intro- 

 mittent or palpal organ, which is often retractile and exceedingly 

 .complicated. At its simplest it is not retractile, and consists of a 

 swollen basal portion or bulb, and of a terminal portion or spine. 

 The legs resemble the palp of the female, but are longer, have 

 simple coxae, an extra segment, the protarsus, between the tibia 

 and tarsus, and two or three claws at the end of the tarsus. 

 The third or inferior claw is usually present when the ungual 

 tufts are absent, absent when they are present. The sternum is 

 usually oval, and supports in front the lower lip or labium ( = pro- 

 sternum). Sometimes the sternum is marked with muscular scars 

 or sigilla. 



The cephalothorax is connected with the abdomen by a narrow 

 .stalk or 



