A SPIDER. 75 



b) The proximal joint of each pedipalp is seen to have a lateral pro- 



jection, the endite. These projections sometimes meet just back 

 of the mouth, in other cases they are not contiguous. Between 

 them is the labium, a sort of lower lip. Look for tufts or brushes 

 of hairs about these organs. Count the number of joints in one 

 of the pedipalps and compare with the number in a leg. 



c) Near the front of the abdomen is a shallow transverse groove at 



the ends of which are the two lung slits, openings leading to the 

 book-lungs. Just in front of the groove at the middle point is 

 the genital opening, called the epigynum in the female. 



d) At the posterior end of the abdomen are the spinnerets occurring 



in pairs. How many pairs ? Determine the number of segments 

 in each spinneret. 



e) Just back of the spinnerets is the anal opening and just ahead of 



the aforesaid organs the tracheal spiracle opening into the 

 respiratory tracheae. 



Exercise 2. Draw the under side of the spider on the same scale as 

 ) omitting all but the proximal joint of legs and pedipalps. 



Technical Note. Detach a leg, a pedipalp, one of the chelicem, and a 

 spinneret. Study these organs with a low power of the microscope. 

 They may be mounted on a slide or viewed in a watch glass. 



THE APPENDAGES. The legs will be found to consist of the follow- 

 ing joints, beginning with the proximal one: coxa, trochanter, 

 femur, patella, tibia, metatarsus, and tarsus. Which one of these 

 is lacking in the pedipalp ? Compare with the leg of an insect, such 

 as a grasshopper or a beetle. Examine the claws at the tip of the 

 tarsus. 



The palpal organ, mentioned above, appears after the last moult 

 of the male and is, therefore, an evidence of maturity. The distal 

 joint of the female pedipalp has no such enlargement. Maturity in 

 this sex is indicated by the appearing of the epigynum after the last 

 moult. 



With a higher power of the microscope one can make out a great 

 many spinning-tubes on the blunt ends of the spinnerets. Some 



6 



