THE NEMERTINE WORMS 



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ing up into pieces at the least touch. The vitality of the severed pieces is so great 

 that the head end has the power to re-form a new tail, and the tail end a new head, 

 and the intermediate pieces a new head and tail. Another common kind is Folia 

 criicigera } so called because its greenish body is marked with five longitudinal white 

 bands and transverse white stripes, forming together a series of crosses. These 

 worms are long and slender, reaching a length of about sixteen inches. The pro- 

 boscis, moreover, when protruded, adds another six inches to their extent. They 

 are found most abundantly in pieces of rock riddled with holes and galleries by bor- 

 ing sponges, and they also intertwine themselves among the prongs of branch- 

 ing corals, as shown in the illustration. 



CROSS-BEARING NEMERTINE (Polia CrUClgerd) ON A CORAI,. 

 (Natural size.) 



Most marine nemer tines prefer rather shallow water; but some occur at con- 

 siderable depths; and a pelagic species from the Indian Ocean, originally described 

 as a mollusk, under the name Pterosoma planum, is a transparent creature, whose 

 internal organs, especially the chestnut-brown digestive apparatus, are visible 

 through the colorless integument. The body diminishes from the front toward the 

 hinder end, and at the sides is marked out by deep notches into a series of five lobes, 

 of which the first pair are enormously large, and have the form of two semicircular 

 wings. The use of these is doubtless to enable the creature to float or swim in the 

 water. All the foregoing are free living types, but we now come to forms (Mala- 

 tobdella} not unfrequently found living parasitically under the gills of various 



