THE SPIDER 



89 



(2) On the ventral side find the appendages. How 

 many in all? How many are legs? How many are mouth 

 parts ? 



Observe the front pair, the mandibles. Are they seg- 

 mented? How do they end at the lower part? How are 

 they attached to the head? What motion or motions have 

 they? These mandibles are called the chelicerae, poison 

 fangs. Near the base is the opening of a duct that leads 

 to a gland which secretes a poisonous substance. This 

 gland is perhaps of the same nature as a salivary gland, 

 and the fluid stuns or paralyzes the prey of the spider. Re- 

 move mandibles with the scissors. 



Behind these are the maxillae, with their palpi. What 

 are the palpi used for? Are they really a necessary part of 

 the spider's mouth parts? Remove the maxillae with scis- 

 sors. Do you find the labium or the labial palpi? 



(3) How many pairs of legs? How are they attached 

 to the body? How many segments? Do the legs of the 

 first pair have as many segments as the others? If the 

 insects have three pairs of legs and labial palpi, and the 

 spiders have four pairs of legs without labial palpi, what 

 does this suggest as to the origin of the extra pair of legs of 

 the spider? Remove the tarsus of one of the legs and put 

 it under the low power of the microscope. What covers 

 the leg? Find three hooks at the end. Observe them close- 

 ly to find the distinct shape of each hook. 



Draw end of tarsus as it appears under the low power 

 objective. 



Have you ever seen spiders with legs missing? Did you 

 ever see them with some legs short? They have the power 

 of reproducing legs when they have lost them by accident. 



