74 A SPIDER. 



you will note that the abdomen is very soft and easily ruptured or 

 crushed. 



b) The eyes arranged in rows on the front part of the cephalothorax. 



Determine the number of these rows, the number of eyes in each 

 row, and compare the eyes in size. With the exception of mem- 

 bers of two small groups, which you are not likely to encounter, 

 all spiders have the same number of eyes as your specimen. If 

 material is at hand compare the arrangement of the eyes with that 

 of other groups of spiders. 



c) The four pairs of legs attached to the cephalothorax. Compare 



in length. How many joints in a leg ? Note the hairs and 

 spines on the legs, as well as on other parts of the body. The 

 colors of the spider are partly due to these hairs, spines, and scales 

 and partly to pigment in the skin. 



d) Projecting downward and forward from the front of the cephalo- 



thorax are the chelicerae, strong jaw-like organs. Each con- 

 sists of a basal piece and a terminal claw in which is a small 

 opening communicating by a duct with a poison gland. Find 

 this opening if possible. Move the claw back and forth, noting 

 that it fits into a groove like the blade of the jack-knife in 

 its handle. 



e) At the sides of and extending beyond the chelicerae are the pedipalps 



resembling a fifth pair of legs, though they really function as acces- 

 sory mouth parts. If your specimen is a mature male the ter- 

 minal joint will end in a complicated knob, the palpal organ. 



f) Connecting the cephalothorax and the abdomen is a more or less 



slender stalk, the pedicle. It is not likely to be visible unless 

 the two body regions be pushed apart slightly. It will not appear 

 in the drawing. 



Exercise i. Draw a dorsal mew of the spider enlarged three to five 

 times. 



A VENTRAL VIEW. In addition to the parts appearing on the dorsal 

 aspect note also, on the under side: 



a) The sternum, a piece fitting in between the basal joints of the legs. 



