64 INVERTEBRATE ZOOLOGY. 



form infesting earth-worms. The adult, often visible to the naked eye. is 

 found in the body cavity, lying along the wall of the alimentary canal. The 

 encysted form, filled with pseudonavicellae, occurs in the speiinatic vesicles 

 and is found in one out of about three or four individuals. 



I I ■ Open an earth-worm along the mid-dorsal line, from the anterior 

 end as far as a thickened girdle of lighter color, the clitellum (aljout the 

 anterior fourth). Pin it <mt in a dissecting pan and examine with the lens. 

 The spermatic vesicles consist of three pairs of very noticeable organs some- 

 what kitlney shaped and covering the alimentary canal dorsally. In infected 

 specimens, minute white flecks may generally be found scattered over the sur- 

 face of these organs, and often on the body wall, and other organs in the vi- 

 cinity. When such a specimen is found, remove to a slide a bit of the infected 

 portion, tease it out a little and press with a cover glass, but not too hard. 

 With oO"" the white flecks may be seen to be cysts filled with pseudonavicellae. 

 These vary greatly in size and number contained. Select a small and clear 

 one and observe separate pseudonavicellae with a high power. Crush a cyst 

 by pressing a needle upon the cover glass ichile under observation. 50-100''. 

 The individiials may thus be isolated and studied separately. 



VI. Bacteria. 



I 2. Collect in a water drop a verj- slight amount of the scum floating 

 upon the top of stagnant water, or water containing decomposing material. 

 Scum from macerating bones is especially good. Cover and observe with high 

 powers. Focus high — i. e. for the upper surface of the laj'er of water. Look 

 for extremely minute sticks and dots lying in all directions. These are stick 

 forms. Bacilhis and Bacterium. The screw form. Spirllhun. is often present. 

 These may all be in active motion or in a quiescent condition. 



I 3. Make a permanent mount of the above, as follows : 



(1) Spread a very thin layer of the material containing Bacteria upon a 

 cover-glass. 



(2) Set aside and allow to dry. 



(3) Hold glass in the fingers, preparation side uppemiost. and pass quickly 

 through an alcohol flame 2-3 times. This coagulates the thin pellicle of albu- 

 men surrounding each individual and thus fastens it to the glass. 



(4) Lay the glass down and place upon it a drop of methyl violet, fuchsin, 

 or methyl blue, and let it stand 3-5 minutes. 



(5) Take the glass in forceps and wash off with stream from wash bottle. 



