THE EARTHWORM. 137 



tive tract, muscular on its outside ; the outer one, the tube 

 formed by the body wall, muscular on its inside. Note 

 that the body cavity between these two is bridged by 

 the numerous transverse septa. Compare the earthworm 

 with the crawfish and the grasshopper in respect to this 

 structure. 



Microscopic Examination. Obtain another anaesthe- 

 tized worm. Insert a slender pointed pipette through a 

 puncture into the body cavity, and draw out a drop of 

 the fluid filling that cavity. Place the drop on a slide, 

 cover, and examine with high power of microscope to 

 discover : 



1. Chloragogue cells, large and irregular, and yellowish 

 in color. These cells form a layer surrounding the ali- 

 mentary canal for a great part of its length. They are 

 believed to perform the functions which the liver per- 

 forms in higher animals, at least to the extent of secreting 

 a fluid to aid in the digestion of food. 



2. Amoeboid blood corpuscles, so transparent they may 

 be overlooked at the first glance. These show pseudo- 

 podia, and, if kept warm, may be seen to be in action, 

 like amoeba, whence the name. It must be borne in mind 

 that these cells do not have an independent existence like 

 amoeba, but that they are constituent cells of a many- 

 celled animal, dependent for their life upon conditions 

 supplied by other parts. 



3. Sperms. Lay open the body cavity. P-uncture one 

 of the seminal vesicles, and take from it with a pipette a 

 drop of its fluid contents. Mount, cover, and examine this 

 with high power of microscope. It should contain many 

 minute filiform sperms, some of which may be seen actively 

 swimming about. They may often be better seen (but 

 not in motion) after running a drop of magenta under 

 the cover. 



