SYNOPSES OF NORTH AMERICAN 
INVERTEBRATES. 
XXI. THE NEMERTEANS. 
WESLEY R. COE. 
PART I. 
SPECIES ÜCCURRING ON THE WEST AND NORTHWEST COASTS OF 
NORTH AMERICA.! 
Tue Nemerteans embrace a highly specialized group of flat- 
worms, the most characteristic features of which are the soft 
extensible body without indication of external segmentation, the 
highly developed eversible proboscis, the straight intestine, open- 
ing at the posterior end of the body, and the absence of any 
distinct body cavity. 
. The body is commonly long, flattened, and ribbon-like 
(Cerebratulus), filiform (Cephalothrix, Lineus), broad and flat 
(Drepanophorus), thick and rounded (Euborlasia), or short and 
cylindrical (Tetrastemma), but in nearly all forms is extremely 
extensible and may often be contracted to one tenth the length 
of the fully extended worm. In size there is the greatest varia- 
tion found in any group of worms, for there are minute species 
(Tetrastemma) but 5 mm. long and a half millimeter thick when 
sexually mature, while another (Zineus longissimus) may become 
1Of the 87 species which have thus far been recorded from the west and 
northwest coasts, only 19 are known to occur on the east coast of North Amer- 
ica or in other regions of the globe. Because of this geographical limitation of 
extent on anatomical 
peculiarities, which liave been somewhat more fully studied in the Pacific species 
than in those from the east coast of North America. 
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