22 The Structure a7id Habits of Spiders. 



the sides to receive the blood, and branches 

 through which it flows to different parts of 

 the body. The greater part of the blood 

 enters at the front of the heart, and passes 

 backward into the abdomen, or forward into 

 the thorax. 



BREATHING-ORGANS. 



In the front of the abdomen are the princi- 

 pal breathing-organs, — a pair of sacs, R, con- 

 taining a number of thin plates, through which 

 the blood passes on its way to the heart. Be- 

 sides these, there is a pair of branching air- 

 tubes, /, opening near the spinnerets. 



NERVOUS SYSTEM. 



The nervous system has a large ganglion, J, 

 in the thorax, from which branches, i, pass to the 

 limbs and abdomen. At the front end two 

 branches extend upward, each side of the 

 oesophagus, to two smaller ganglia, k, from 

 which pass nerves to the mandibles and eyes. 



The reproductive organs, S, lie along the 

 under side of the abdomen, and open between 

 the two air-sacs. 



