PARKER. — THE SENSORY REACTIONS OF AMPHIOXUS. 427 



usually rests with its tail out of the sand, a statement repeated by 

 Krause ("83, pp. 132, 135). Subsequently and without explanation 

 both Steiner ('88, p. 41) and Krause ('97, p. 513) abandoned this 

 opinion for the opposite one. That the animals ordinarily rest with 

 the anterior end out of the sand was the opinion of J. Miiller ('41, 

 p. 399 ; '44, p. 84), Nlisslin ('77, p. 18), Rohon ('82, p. 37), Willey 

 ('94, p. 9), Nagel ('96, p, 79), and others, and any one who carefully 

 inspects a number of lancelets at rest will soon be convinced that this 

 is the normal position. Although the extruded anterior end is the 

 portion of the animal least sensitive to light, lancelets in their resting 

 positions in ordinary sand will respond quickly enough to this stimulus. 

 Thus in a large dish of coral sand, over which there were a few inches 

 of sea water, the anterior ends of twenty-three lancelets were counted 

 in dim light. As a result of throwing on a beam of very strong light, 

 most of the heads were quickly withdrawn under the sand, only two 

 remaining visible. This reaction is doubtless dependent on the stimu- 

 lation of the most anterior eye-cups, and as a rule the resting position 

 of the animal is such that this naturally occurs. 



The negative phototropism of amphioxus has led to the belief that 

 during the day it remains buried in the sand, except perhaps for its 

 anterior end, but that during the night it leaves the sand and leads 

 a more active existence. W. Miiller ('74, p. 7) states that Branchi- 

 ostoma lanceolatum is nocturnal, and at twilight comes to the surface 

 of the sandbank in which during the day it is buried. Rice ('SO, p. 9) 

 mentions that individuals of this species which were seen swimming 

 at night in the Naples Aquarium were quiescent in the daytime, and 

 Rohon ('82, p. 36) and Krause ('97, p. 513) also speak of this species 

 as having nocturnal habits. B. caribbaeum showed no evidence of 

 such habits. All inspections of the aquaria that I made after night- 

 fall, and with caution as far as light was concerned, demonstrated that 

 the lancelets remained in the same position in the dark as in the light. 

 Further, several glass vessels containing coral sand and known numbers 

 of lancelets that were sunk over night to the natural level of the sand 

 in the bed of the inlet, contained, when taken up the next day, the 

 same numbers of animals, thus indicating that the lancelets had re- 

 mained buried and had not come out on the surface of the sand, where 

 the current would surely have swept them away, even supposing that 

 they had not started swimming. Although this experiment was tried 

 only a few times, the results always led to the same conclusion, and it 

 therefore seems probable that at least B. caribbaeum is essentially a 

 burrowing animal, and that it leaves its native sand only when forced 

 to by the accidental action of currents, etc. 



