COE : XEMERTEANS <)F WEST AND NORTHWEST COASTS. 5 



all forms is exceedingly contractile, and may often be contracted to 

 one tenth the length of the fully extended worm. In size there is 

 the greatest variation found in any group of worms, for there are 

 minute species (Tetrastemma) but 5 mm. long and a half milli- 

 meter thick when sexually mature, while another form (Linens 

 longissimus) may become 25 meters in length when fully extended, 

 but is of very slender proportions; ^wother {< ^erebratuliis lacteus) 

 may become 7 meters long and 20 mm. wide, while the single known 

 individual of a species described in this report {I'Juborlasia maxima) 

 was 45 mm. in width after preservation. 



Body. — The body of the nemertean is without external segmen- 

 tation, although many of the internal organs are metamerically 

 arranged ; and it is devoid of setae, parapodia, or other external 

 appendages (except in a single known species, Nectonemertes). 

 The body is covered throughout with glandular and ciliated cells, 

 as in the Turbellaria. A true body cavity is wanting, the space 

 between the muscular walls of the body and the intestine being 

 filled with gelatinous tissue, or parenchyma. 



Alimentary canal. — The mouth is situated anterioi'ly either in 

 front of the brain in the Hoplonemertea, or immediately behind it 

 in the other two orders. The alimentary canal extends the whole 

 length of the body, being in most of the genera provided with 

 paired lateral diverticula, and sometimes with other appendages, 

 and having the anus at the posterior end of the body. 



Blood system. — The blood vascular system consists of a pair of 

 closed lateral vessels extending the whole length of the body, to- 

 gether with a similar median dorsal vessel in most forms; these are 

 all connected in the head by anastomosing lacunae, and in many 

 species are united throughout the intestinal region by regularly 

 arranged transvei-se vessels situated above and immediately outside 

 the intestinal diverticula. In certain genera there are additional 

 vessels and lacunae in the esophageal region. The blood vessels are 

 usually without muscular walls, the blood itself, with its contained 

 corpuscles, which are sometimes colorless and sometimes red in 

 color, being circulated back and forth in the same vessels through 

 the body by the general contractions of the body musculature. 



JSfephridia.— The excretory S3'stem usually consists of a pair of 

 lateral canals with numerous branches, which sometimes end in 

 so-called "flame " cells, similar to those of the Turbellaria, and enter 



