178 GENERAL BIOLOGY 



Another and very peculiar mode of waste disposal occurs 

 in the worm. The cells of the peritoneum, where they cover 

 the parts chiefly concerned with the elaboration of the food, 

 (stomach-intestine and larger blood vessels leading forward 

 therefrom) instead of remaining thin and flat become elevated 

 into high pear-shaped sac-like bodies attached by their 

 slender pointed ends, and filled more or less completely with 

 yellowish-green granules of a substance called chloragogue. 

 It is not quite certain what is the nature of these granules 

 but they are believed to be waste nitrogenous products, 

 and it is certain that they accumulate in the cells until the 

 cells are distended and burst. Then they fall free into the 

 body cavity. A drop of the body fluid taken at random 

 with a pipette from an adult worm is certain to contain num- 

 bers of these isolated greenish-yellow granules. They filter 

 posteriorly through the holes in the septa, and finally accu- 

 mulate in little brownish lumps, intermixed with dislodged 

 setae, in a few of the hindmost segments. There they 

 are consumed by commensal nematodes. The blood always 

 contains, besides these granules and leucocytes already men- 

 tioned, great numbers of bacteria, which the latter feed 

 upon, and occasional parasites. 



Study 24. The general structure of the earthworm. 



Materials needed : Live worms of large size ; specimens 

 well preserved and hardened : small dissecting trays and tools. 



Study the live worm, its movements, its sensibility to 

 touch, the way it uses its setae. Turn it over and watch it 

 right itself. Note all external features. 



In a freshly opened worm make a general survey of the 

 internal organs, guided by the description of the preceding 

 pages in the following order: alimentary canal, circulatory 

 system, nervous system, reproductive organs, excretory 

 organs. Then remove these organs and observe in the body 



