148 TURBELLARI&. PART in. 



species are not parasitic. These are often united in 

 swarming masses that nestle in mud, wet moss, wet 

 earth, and aquatic plants. One species causes the cockle 

 in wheat, appearing like a living tuft of white wool in 

 the blackened grains. They appear in sour paste and in 

 other decomposing substances, and are so tenacious of 

 life that, after being completely dried for months, and 

 apparently dead, they revive on being moistened. 



Turbellarice. 



The Turbellarise are fresh- and salt-water animals, 

 distinguished by having the whole surface of their 

 bodies covered by cilia, under which in some species 

 there are thread-cells containing six, eight, or a greater 

 number of darts. Most of the members of this tribe 

 have elongated flattened bodies, and move by a sort of 

 crawling or gliding motion over the surface of aquatic 

 plants and animals. Some of the smaller kinds are 

 sufficiently transparent to allow their internal structure 

 to be seen by transmitted light. The mouth, which is 

 situated at a considerable distance from the rounded 

 end of the body, opens into a sort of gullet leading into 

 the stomach, which has no other orifice, but a great 

 number of branching canals are prolonged from it, 

 which carry its contents into every part of the body. 

 A pair of oval nerve-centres are placed near the 

 rounded end of the animal, whence nerves extend to 

 various parts of the body ; and near to these there are 

 from two to forty rudimentary eyes according to the 

 species, each of which has its crystalline lens, its pig- 

 ment layer, nerve bulb, and its cornea. The power of 

 the Planaria to reproduce portions which have been 

 removed is but little inferior to that of the Hydra. 



