THE ARTHROPODS 



377 



Appendages : No antennas. Compare the eyes (6 or 8) with those 

 of crayfish. The anterior mouth-appendages are the mandibles (or 

 chelicerse), the posterior ones are maxillas (or pedipalpi). Each 

 maxilla has a long feeler (palpus). The mandibles are hollow and 

 at their tips are the openings of the poison-glands. How many 

 walking legs ? Compare number of legs with those of crayfish. Are 

 there appendages on abdomen ? 



In some species of spiders transverse bands on abdomen are 

 supposed to indicate former segmentation. This may be seen in a 

 scorpion. On ventral side of abdo- 

 men : (1) External openings of lung- 

 sacs are, in common spiders, one on 

 either side of anterior portion of ab- 

 domen. (2) Between these are the 

 openings of the reproductive organs. 

 (3) Two or three pairs of papillae 

 (spinnerets) are at posterior end of 

 abdomen note that these are seg- 

 mented like legs. (4) A spiracle 

 (breathing pore) is just in front of the 

 spinnerets in some spiders. (5) The 

 posterior opening (anus) of the ali- 

 mentary canal lies behind the spin- 

 nerets. 



Make drawings of spider from dor- 

 sal and ventral views. 



Observe the habits of living spiders 

 in fields and in vivaria. Keep spiders' 

 eggs under observation until hatching, 

 and then observe habits of the young, especially spinning. 



How are spiders distinguished from Crustacea ? In what respects 

 are they similar ? 



319. Other Arachnids. The scorpions live in warm coun- 

 tries. They have a sting at the end of the " tail " (which is 

 part of the abdomen), and they use it for poisoning their prey, 

 chiefly insects and spiders. Some of the large ones, six to 

 eight inches long, can seriously poison man, and the sting 

 of even the small ones is painful. This general form (see Fig. 

 129) suggests a similarity to a lobster ; but the large pincers 

 of the scorpion correspond to the jaws or mandibles of crus- 



FIG. 128. Common spider 

 (Epeira diadema). Note four 

 pairs of legs, while insects have 

 three. The abdomen is much 

 larger than the cephalothorax. 

 (From Parker and Haswell.) 



