CONCLUDING OBSERVATIONS. 



367 



Fig. 277. 



tertaining. Some propel themselves directly forward 

 with a velocity which appears (when thus highly magni- 

 fied) like that of an arrow, so that the eye can scarcely 

 follow their movement ; while others drag their bodies 

 slowly along, like the Leech. Some make a fixed point 

 of some portion of the body, and revolve around it with 

 great rapidity ; while others scarcely present any appear- 

 ance of animal motion. Some move forward by a uni- 

 form series of gentle undulations or vibrations ; while 

 others seem to perform consecutive leaps, of no small ex- 

 tent compared with the length of their bodies. In some 

 instances the body is furnished with stiff bristles and 

 hooks, by the agency of which the animalcule is enabled 

 to run and leap upon the stems and leaves of aquatic 

 plants. In short, there is scarcely any kind of movement 

 which is not practiced by these animalcules. They have 

 evidently the power of steering clear of obstacles in their 

 course, and of avoiding each other when swimming in 

 close proximity. By what kind of sensibility the wonder- 

 ful precision and accuracy of their movements is guided 

 is yet very doubtful." One of the most singular of these 

 Infusoria is the Baccillaria Paradoxa, which is composed 

 of several parts arranged like a sliding ruler. It moves 

 along by sliding these parts upon each other, first thrust- 

 ing them forward, then closing those in the rear upon the 

 part farthest in front. 



