WORMS. 



53 



can see no organs of locomotion, and yet these animals glide smoothly 

 along. The microscope, however, shows that they move by means of cilia, 

 very like those of the ciliated protozoans described on a preceding page. 

 If carefully watched, the process of feeding can be seen. From the under 

 surface (not shown in the cut, but a similar structure exists in Figure 52) 

 is a long, extensible proboscis, which can be turned in every direction in 

 search of food. These animals eat everything small enough to enter the 

 proboscis ; and as a good deal of mud enters with the food, the result is 

 that the outline of the digestive tract in the transparent forms can be 

 clearly seen through the walls of 

 the body. It is not a simple tube 

 in the Planarians, but is rather a 

 blind pouch, from which numerous 

 lateral pouches are given off. 



Some of the marine forms are 

 much larger than the terrestrial 

 ones, the figure here shown illus- 

 trating a form which attains a 

 length of an inch. It is repre- 

 sented as crawling upon a bit of 

 sea-weed, the anterior end of the 

 body being upturned and showing 

 the two very sensitive tentacles. 

 Only one of the land planarians 

 has as yet been described from 

 the United States, but in Europe 

 several are known ; their home 

 seems to be in the tropics, South 

 America possessing twenty-seven 



Of the Sixty-four known Species. Fig. 51.-- A marine planarian {Th. 



Associated with both the fresh-water and the marine planarians are 

 other worms, which differ in having a straight, unbranched digestive tract. 

 One of these forms from fresh water is illustrated here, greatly enlarged 

 (Fig. 52). The cut shows the cilia covering the whole surface of the body. 

 the large proboscis, two eggs (large, dark-colored bodies on the left of the 

 figure), as well as other structures. In still others of the fresh-water 

 species, the body divides transversely to form new individuals, and fre- 

 quently a second or even a third division will begin before the first is com- 

 plete, and the result is a compound worm with several mouths repeated in 

 serial order. It is a process which recalls the formation of jelly-fishes by 

 division of a hydroid-like stock, as described on page 22. 



