10 SPIDERS [CH. 







the mechanism by which that operation is performed 

 is of quite a different nature. 



Having, then, very readily determined our speci- 

 men to be a true spider, we may as well use it to 

 note some further structural points the detailed 

 examination of which may be deferred till we have 

 considered their functions. Note the jaws orchelicerae, 

 consisting of a stout basal part and a fang which, 

 when not in use, is shut down like the blade of a 

 knife ; note the pedipalps or feelers, exactly like 

 small legs, but showing by their action that their 

 function is sensory and not locomotor. If they are 

 knobbed at the end, the specimen is a male, otherwise 

 it is a female or as yet immature. Look closely at 

 the front part of the cephalothorax, and several eyes 

 will be visible probably eight. They are not 

 compound divided into innumerable facets, like 

 those of insects but simple and smooth, though to 

 make sure of this the use of a microscope would be 

 necessary. Finally, obtain a view of the under 

 surface of the abdomen, and note in front, on either 

 side of the middle line, two semilunar patches of a 

 lighter colour. These are the " lung-books," -special 

 breathing organs peculiar to these animals ; two is 

 the usual number, though certain spiders possess a 

 second pair behind the first. 



But the spinning mammillae or spinnerets are 

 still more "characteristic and more easily seen, though, 



