No. 4.] NORTH-AMERICAN ECHIURIDS. 



167 



thereby half or three-quarters of an inch. The two anal rows 

 of setae now serve to hold it in position, while the anterior end 

 is again thrust forward and downward into the mud, and the 

 ventral setae are fastened in a new position. This process is 

 repeated until the animal finally disappears beneath the sur- 

 face, leaving a circular opening equal in diameter to the body 

 at its greatest lateral contraction. The whole process is ex- 

 tremely slow, and fully forty minutes are consumed in getting 

 the posterior end of the body out of sight beneath the surface. 



The burrow proceeds diagonally downward for ten to eight- 

 een inches, then runs horizontally from six inches to two or 

 three feet, and finally turns vertically upward again toward the 

 surface. 



When the animal reaches the surface the anterior end of the 

 body is pushed out far enough to free the proboscis. This is 

 then restored to its normal position and the body is withdrawn 

 again into the burrow. 



Spengel notes (15) that each burrow of the species {E. Pal- 

 lasii) observed by him at Nordenay possessed two openings 

 close together and each surrounded by a low wall. But those 

 burrows were made in hard sand, while these are in soft mud, 

 and consequently we should expect to find differences. These 

 burrows at first have two openings, but the original entrance 

 soon fills up through the caving in of its walls and the washing 

 in of mud from the surface. The entire diagonal portion is 

 often filled in this way and is never opened again, leaving this 

 end of the burrow blind. These burrows also, when first 

 formed, have low walls around the openings, caused by the 

 pushing aside of the mud, but they quickly disappear. 



The Echiurus assumes a position just below the surface, hold- 

 ing itself in place by the two rows of anal bristles {cf. Shipley). 

 The mud then washes into the burrow and forms a plug one to 

 two inches thick, with a small opening about the size of a lead- 

 pencil at the center. Through this opening the proboscis is 

 thrust out in search of food when the tide is in, and is then 

 the only portion of the animal which is visible. It is capable 

 of great extension, as was the proboscis of B. viridis described 

 by Eisig, and often reaches a length of five or six inches. The 



