VERMES 



157 



pin head works its 

 way through the 

 walls of the fish's 

 intestine to the 

 muscles, remains 

 several months 

 quiescent until 

 spring, when it 

 again enters the 

 i n t e s t i n e and 

 passes out into the 

 water. Its length 

 at this time is 

 about an inch. 



In a few weeks it reaches full size. The young of those 

 species laying eggs in the damp earth bore into caterpillars, 

 grasshoppers, locusts, and beetles. During the months 

 of August, September, and October hair worms may some- 

 times be found in the locusts by pulling open the abdom- 

 inal cavity with forceps or needles. 



FIG. 183. Horse-hair snake. Photograph twice 

 natural size. 



Platyhelminthes or Flatworms 



The flatworms are remarkable for their variation in 

 size. Some of them living parasitic on the gills of fish 

 and the king crab are only one or two millimeters long, 

 while the tapeworms parasitic in man reach a length of 

 fifty feet. Many members of this phylum are parasites 

 and all have soft bodies usually much flattened dorso- 

 ventrally. There is no body cavity (ccelome) surrounding 



