110 



CHAS. B. WILSON. 



end of its burrow by turning it abruptly upward to the sur- 

 face, and then lies with its head in the lower part of this 

 vertical portion. The burrow around the head and in the 

 immediate vicinity is enlarged somewhat, so that the water 

 can circulate freely, and by alternately swallowing and eject- 

 ing mouthfuls of water the Nemertean generates a very per- 

 ceptible current. 



The swallowing is long and slow, while the ejection is 

 short and abrupt, the two together occupying about ten 

 seconds. This is evidently the Nemertean's mode of breath- 

 ing, and the purification of the blood must take place in the 

 walls of the oesophagus, as we should naturally infer from 

 the arrangement of the circulatory system. These facts, of 

 course, were chiefly gathered from specimens kept in an 

 aquarium where the supply of water was constant, but it was 

 curious to note that they alternated periods of rest with 

 periods of breathing exactly as if they had been subject to 

 the flow of the tide. And their periods of rest usually, 

 though not always, corresponded closely with those of the 

 ebb tide. 



During the breathing the cephalic slits along the sides of 

 the head were occasionally, though not regularly, opened 

 and closed. At such times, of course, a current of water 

 would enter the side-organs, and it is possible that they 

 assist somewhat in the purification of the blood. But from 

 the regularity of movement in the oesophagus and the entire 

 lack of it in the cephalic slits, we must conclude that the 

 former constitutes the true respiration. 



Locomotion. — The mode of locomotion by means of 

 which the Nemertean moves through its burrow has already 

 been described. 



They also come out of their burrows at times and swim 

 about in the water. Yerrill states (46) that while swim- 

 ming the body is turned up edgewise and thrown into many 

 undulations, and the motion resembles that of an eel, but is 

 less rapid.^^ Coe adds (15) that it is often met with at 

 night swimming near the surface of the water,'' This is a 



