iv: 



ZOOLOGY 



The method of spinning deserves careful attention. The 

 spinning-organs consist of a set of glands Ijdng in the hinder 

 part of the abdomen, and opening to the exterior through 

 a number — often several hundred — of spinning " spools." 



These spools are the modi- 

 fied mouths of glands, and 

 are grouped upon and be- 

 tween tubercles called spin- 

 nerets. The secretions of 

 the glands, as they are poured 

 out into the air, fuse together 

 and harden into a thread. 

 The thickness of the thread 

 is determined by the number 

 of glands secreting together. 

 The economic importance 

 of spider webs is consider- 

 able. First of all, they are of 

 the greatest importance in 

 capturing many destructive 

 insects, such as flies, mosqui- 

 toes, and moths. Another use to which they have been 

 put is in making silk cloth. The silk of the spider is smoother 

 and glossier than that of the silkworm, but it is much harder to 

 collect in quantity. A spool is passed against the spinnerets of 

 an individual spider and slowly revolved, winding the silk upon 

 it. The difficulty comes in rearing the spiders, for they are ex- 

 tremely voracious, and if the sujjply of flies is insufficient, they 

 attack and devour one another. Consequently they must be 

 kept isolated and fed individually, and yet yield in the end onlj^ 

 an ounce or so (about 30 grammes) of silk. Other uses of spiders' 



Fig. 11.3. — Thomisus, a crab spider. 

 Diagram showing arrangement of eyes 

 at bottom of figure. From Emerton. 



