INTERNAL ORGANS. 87 



pillars are the silk- vessels ; these have a distinct 

 outlet on the under lip, which becomes modified 

 to form a spinneret ; from this point a delicate 

 thread runs along the oesophagus to the middle 

 or end of the thoracic part of the body ; there it 

 thickens to form the secreting vessel, a slender 

 flattened riband, running in the same direction 

 along the sides of the alimentary canal to about the 

 middle of the stomach, when it turns a little upon 

 its course, again reverses its direction, and pass- 

 ing above the stomach, continues to its extremity. 



Finally the reproductive system, which relates 

 to the species rather than to the individual, is of 

 extreme simplicity ; it consists mainly of a pair 

 of very minute bodies, either a chambered gland 

 or a consolidated bunch of tubes, forming a sort 

 of sac ; these bodies are situated on either side 

 of the fifth abdominal segment ; from each of 

 them proceeds a thread which runs back a little 

 way, and then down and back along the sides of 

 the body until it has nearly reached the middle 

 line beneath, when it passes through a special 

 band of muscle, and, side by side with its mate, 

 terminates in a common blind sac, situated just 

 beneath the extremity of the intestinal canal. 



The nutriment received into the body is not all 

 absorbed by the formation and continual repair of 

 organs and muscular tissue ; and when the sup- 

 ply is greater than the need, the residue is stored 



