PLATYHELMINTHES 85 



Class (or Phylum) Nemertinea. (Gr. nemertes, true).— The 

 Nemerteans are soft, contractile, chiefly marine flatworms some- 

 times classed with the Turbellarian Platyhelminthes. They range 

 in length from 5 mm. to 90 feet. 



The mouth is anterior and ventral and the anus is posterior. 

 They have an eversible proboscis armed with stylets, indicating that 

 it is functional both as a tactile and an ofl'ensive or food-t'aking 

 organ. The digestive tract consists of an esophagus, stomach, 

 intestine with paired diverticula or a long cecum, and a rectum. 

 The circulatory system, not found in Platyhelminthes, consists of 

 two or three longitudinal trunks with connecting branches. The 

 blood sometimes contains hemoglobin. Excretion is effected 

 through paired and many-branched longitudinal canals which open 

 to the outside through pores. Most nemerteans are unisexual, 

 and a few are hermaphroditic. The paired gonads discharge their 

 products through the body wall, having no permanent genital ducts, 

 A few are viviparous. Development is direct or in some forms by 

 the metamorphosis of a free swimming larva, the pilidium (Desor's 

 larva). (See p. 220.) The nervous system consists of a four-lobed 

 brain with a pair of large lateral nerves uniting at the posterior end 

 of the body, a dorsal median nerve, and, in some, a ventral median 

 nerve. There are lateral ciliated cerebral canals related to the 

 dorsal cerebral lobes. Certain species have as many as two hundred 

 ocelli equipped with a lens and nerve, while others have two otolithic 

 vesicles. 



Nemerteans are carnivorous, and feed on soft-bodied inverte- 

 brates, certain large species capturing tubiculous worms. A few 

 are parasitic, infesting Crustacea and mollusca, while others are 

 commensals in the pharynx and atrial cavities of tunicates. 



References on Platyhelminthes 



Fantham, Stevens and Theobald's (1920) Translation of Braun's 



Thierischen Parasiten des Menschen. 

 Linton, E. Many papers published by the U. S. Bureau of Fisheries. 

 Stiles, C. W. Cestode Parasites of Man. Bulletins 25 and 28, U. S. 



Hygienic Laboratory. 

 Stiles and Hassall. The Inspection of Meats for Animal Parasites. 



Bulletin 19, U. S. Dept. of Agriculture. 

 Stunkard, H. W. Many papers listed in his bibliography, New York 



University. 



