How Animals Work. 



body, called spiracles. A spider, in addition to these 

 air-tubes, has generally two or four so-called " lung- 

 books " to help it to breathe. We never find a spider 

 with the great compound eyes made up of many cells 

 or facets which are such a characteristic of insect 

 anatomy, the spider being provided only with a series 

 of simple, single eyes, bead-like, and arranged in two 

 rows on the front of the head. Finally, a spider does 

 not pass through a well-marked series of changes or 

 transformations larva, pupa, adult as do most of the 

 true insects, the newly born baby spider resembling 

 the adult in all essential features. These are all notice- 

 able features of distinction by which the reader can 

 readily realize the difference between a spider and a 

 true insect. 



For the production of the silk used in the build- 

 ing of her snare or nest the spider has on the end of 

 her body a series of glands, or " spinnerets " as they 

 are called, composed of quantities of little tubes, through 

 which the liquid secretion of which the silk is formed 

 passes out, becoming solidified into the fine silken 

 thread on coming in contact with the air. The spider 

 can use just as many of her spinnerets at a time as she 

 considers necessary, and therefore can vary the quality 

 and thickness of the thread to meet her requirements. 

 The feet or claws of the spider are wonderfully modified 

 and adapted to aid her in the work of building her web : 

 they are comb-like in appearance, the little combs being 

 deftly employed in drawing out the threads when the 

 weaving of the snare is in progress, or the cocoon in 

 which she deposits her eggs is being made. These 

 highly specialized claws are also used to seize and hold 



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