T HE FLATWORMS— PLATYHELMINTHES 145 



with a sharp razor blade, each half will regenerate the missing- half and 

 the result is a two-headed animal. These two can then be split to give 

 four, and an eight-headed planaria has been produced by a splitting of 

 the four. Grafting is also possible just as it is in plants ; a part of one 

 animal can be cut off and placed in an incision of another animal and it 

 will grow there. 



The regenerative power of the planaria also enables it to survive long 

 periods without food. If you are the type that forgets to feed the cat or 

 the canary, you should keep planarians for pets. They can live for nine 

 months without food. During this time they derive nourishment from 

 their own body, starting with their reproductive organs and then other 

 parts as needed. They may shrink from a half an inch to about one 



Photo by Winchester 



Fig. 10.7. Regeneration of planaria. The posterior end of this animal was slit 

 longitudinally. Regeneration produced this condition. 



seventh of an inch during this long fast, but when food again becomes 

 available they quickly restore the tissues which have been absorbed for 

 nourishment and are no worse for the experience. To a certain extent, 

 all animals utilize their own body tissues for nourishment during times 

 of starvation. A glance at pictures of starving human beings shows 

 the emaciation that develops as food is drawn from the various parts 

 of the body. Of course, entire organs are not lost as in planaria, for 

 man could not regenerate them if they were. However, a starving per- 

 son may lose as much as one half of his body weight due to this process 

 and still be restored to a normal state when he can again eat properly. 



Flukes — The Trematoda 



Members of the class Trematoda are commonly called flukes. They 

 have a body structure somewhat like planaria, but they are all parasitic 

 rather than free-living forms. They parasitize many parts of the 

 bodies of higher animals — there are blood flukes, lung flukes, liver 

 flukes, intestinal flukes, and even some that cling to the external surface 



