Chap. 27 AN AQUATIC MISCELLANY 535 



ulus hercLileus) of the CaHfornian coast is 12 feet long contracted and an esti- 

 mated 75 feet when expanded. The length of outstretched ribbon worms is 

 partly due to the extended proboscis that commonly reaches forward two or 

 more times the length of the body. Not all ribbon worms are so long; some are 

 minute and many measure but a few inches. Like flatworms, some are strongly 

 colored and patterned, many are pale and the species are difficult to identify. 

 The proboscis usually marks them as ribbon worms. 



Unique Features. Proboscis. The ribbon worms' unique and surprising 

 feature is the protrusible proboscis that shoots rapidly forward, comes in con- 

 tact with some hapless clamworm (Nereis), twines around it, and shortening 

 again, pulls the prey back to its mouth (Fig. 27.2). Then the proboscis and 

 the clamworm both disappear. It is as if an elephant could roll its trunk out 



Fig. 27.2. Ribbon worm, Linens socialis, 10 inches or more long, its body con- 

 tracted in a characteristic close spiral. Ribbon worms prey upon clamworms that 

 live among the tide washed seaweeds. (From original of figure 1, Wesley R. Coe, 

 /. Exp. ZooL, 54:416.) 



of a short upper lip, catch a peanut on it, and telescope it inside again. When 

 the wandering ribbon worm (Paranemertes peregrina) of the Pacific Coast 

 comes upon the tunnel of an annelid it extends its slender proboscis through 

 it, like a "plumber's snake," finally winds it about the annelid owner and pulls 

 the latter out. The proboscis is withdrawn by the shortening of a retractile 

 muscle and pushed out when the walls of its sheath are contracted upon the 

 fluid in the sheath. 



Regeneration. Ribbon worms have exuberant powers of regeneration. 

 They break easily, but they more than make up for this in their mending. 

 Those of different species vary greatly in the freedom with which they frag- 

 ment; some break into many pieces whenever they are touched. The hinder 

 parts of mature worms commonly break up spontaneously into pieces which 

 regenerate into perfect individuals, the regular method of asexual reproduction. 

 Many experiments in regeneration have been made upon ribbon worms by 

 W. R. Coe especially upon Linens socialis of the Atlantic and Linens vegetiis 

 of the Pacific Coast (Figs. 27.3, 27.4). If a worm 100 mm. long is cut into 

 100 pieces, each one mm. long, they will develop into an equal number of 

 minute worms in four to five weeks. Regenerated worms like whole ones can 



