CONCLUDING OBSERVATIONS. 367 
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. 
