164 



COLLEGE ZOOLOGY 



Normal worm 





Id 



Figure 86. Lineus: regeneration in a ribbon worm. A, section cut from body. B, its appearance 

 after 12 days. C, the same after 30 days, cut in 3 pieces. Successive cuttings and regenerations 

 indicated by arrows. This worm occurs around Long Island Sound. (After Coe.) 



weed. Locomotion is effected by the cilia 

 which cover the surface of the body, by 

 contractions of the body muscles, or by the 

 attachment of the proboscis and a subse- 

 quent drawing forward of the body. The 

 adults have great powers of regeneration 

 and some reproduce in warm weather by 

 fragmentation of the body (Fig. 86). If, for 

 example, Lineus socialis, which is only 100 

 mm. in length, is cut into as many as 100 

 pieces, each piece will regenerate a minute 

 worm within four or five weeks. These mi- 

 nute worms may again be cut into pieces 

 that regenerate, and these in turn may be 

 cut up, and so on, until miniature worms 

 result which are less than ^-200.000 the vol- 

 ume of the original worm. 



PHYLUM ROTIFERA 

 (ROTATORIA) 



The Rotifera or Rotatoria are commonly 

 known as wheel animals (Fig. 87) . The com- 

 mon name refers to the beating of the cilia 

 on the head, which suggests the rotation of 

 wheels. These cilia aid in locomotion and 

 draw food into the mouth. The rotifers are, 

 generally speaking, the smallest of the Meta- 



zoa. Because the rotifers possess fantastic 

 forms and brilliant colors they usually at- 

 tract the attention of amateur microsco- 

 pists. Most are inhabitants of fresh water, 

 but some are marine, and a few parasitic. 

 The tail-like foot is often forked and ad- 

 heres to objects by means of a secretion 

 from the cement glands. The body is usu- 

 ally cylindrical and is covered by a shell-like 

 cuticle. 



Protozoa, other minute organisms, and 

 debris, used as food, are swept by the cilia 

 through the mouth into the pharynx, the 

 lower end of which forms the very charac- 

 teristic grinding organ called the mastax. 

 Here chitinlike jaws, which are constantly 

 at work, break up the food. The movements 

 of these jaws easily distinguish a living 

 rotifer from other animals. A short esoph- 

 agus leads into the stomach. The food 

 is digested in the glandular stomach, or in 

 the stomach and intestine, depending on 

 the species. Undigested particles pass 

 through the intestine into the cloaca and 

 out of the cloacal opening ("anus"). The 

 excretory system consists of two long tubes 

 with flame cells at intervals along their 

 sides. These tubes open into a bladder 

 which contracts at intervals, forcing the 



