ARTHROPODS AND MOLLUSCS 



169 



from which run radii to the outer edges of the web. Around 

 the hub is an open or free zone, and farther out a spiral zone, 

 so called because a line running in close spiral turns fills in 

 the space between the radii. This is the real prey-catching 

 part of the snare, and the silken line here is sticky, while the 

 radii and some other parts of the web are made of silk that 

 is not sticky. The web is supported by strong foundation- 

 lines, attached to 

 leaves, stems, or what- 

 ever is firm in the 

 neighborhood of the 

 web. The spider 

 either rests on the web 

 usually in the centre, 

 or lies concealed in 

 a nest or tent near 

 at hand from which 

 a special path-line 

 runs to the centre 

 of the web. The 

 building of one of 

 these orb webs is a 

 great work, and is 

 done with extraordi- 

 nary nicety of manipulation by the use of feet and spinnerets. 



For an account of web-making, etc., see McCook's "American 

 Spiders and their Spinning Work." 



The habits and instincts of spiders in connection with the care of 

 the young, the building of webs and nests, ballooning by means of silken 

 lines, the active stalking and catching of prey, etc., are very interesting 

 and offer a good field for independent observation and study by the 

 student. McCook's book will be the best guide for this study. 



Mussels, oysters, snails, "sea shells" and cuttlefish 

 (Branch Mollusca).— The molluscs are not to be mistaken 

 for any other of the lower animals; they have a structure 



Fig. 82. Argiope sp., a large orb-weaver 

 (Epeirid). (Natural size; after Jenkins 

 and Kellogg.) 



