No. 4.] NORTH-AMERICAN ECHIURIDS. 169 



Movements and Locomotion. - - In life, even when out of its 

 burrow, the creature is constantly altering its outward form by 

 energetic contractions of the skin muscles, as noted by Greef 

 (6). Deep constrictions appear at various places, which move 

 now forward, now backward, that portion of the body just in 

 front of or behind the constriction increasing proportionately 

 in size. The proboscis is also kept in constant motion, coiling 

 up and uncoiling, rolling inward from the edges and unrolling 

 or stretching out to a considerable distance and then being 

 withdrawn. In its burrow the animal cannot turn around, but 

 can move either forward or backward at will and with equal 

 rapidity. This motion is accomplished by a series of wave-like 

 contractions and relaxations in the circular and longitudinal 

 muscles of the body wall, the one alternating with the other, 

 and both together producing a fairly rapid gliding motion. The 

 necessary rigidity is given to that portion of the body wall 

 which for the time being serves as a fulcrum, by the pressure 

 of the liquid in the body cavity, as first noted by Ouatrefages 

 (9). Andrews has clearly stated (i) the essential factors in 

 the mechanism of Sipnncnlns Gonldii which bring about such 

 " hydrostatic locomotion," and several authors have described 

 similar motion in other gephyreans. 



But no one, so far as known, has suggested any other mode 

 of moving about. Indeed, one of the best recent text-books 

 distinctly states that " the gephyrea are only capable of a very 

 slow creeping motion " (Parker and Haswell, p. 461). 



It seems never to have been suggested to any one, the pres- 

 ent author included, that this same rhythmic contraction of the 

 body walls would furnish an excellent means for swimming. 



Hence it was quite a surprise, on visiting an aquarium after 

 dark during the second summer, to find three or four specimens 

 swimming about in it freely. The body was elongated to twice 

 its ordinary length, while the proboscis was elongated even 

 more in proportion and its edges were rolled downward and 

 inward so as nearly to meet along the median line and form a 

 long narrow tube which seemed to take an active part in the 



swimming. 



The resultant motion was peculiar, being gyratory or cork- 



