PARKER. — THE SENSORY REACTIONS OF AlVIPHIOXUS. 433 



'73, p. 52), and secondly, many sound vibrations can be sensed through 

 our tactile organs as well as our ears. 



That mechanical stimulation serves as a basis for thigmotropic, geo- 

 tropic, and even rheotropic reactions cannot be doubted, though Lyon 

 (:05) has shown that rheotropism in certain fishes depends more upon 

 sight than upon touch. All three kinds of reactions are shown by 

 amphioxus. 



The thigmotropism of amphioxus is evident from the following ex- 

 periments. Ten amphioxus were liberated in a flat-bottomed glass 

 aquarium containing a depth of 10 centimeters of sea water and five 

 centimeters of coral sand. After half an hour all the animals had 

 buried themselves in the sand, and after an hour and a half seven of 

 them had come to rest with their anterior ends a little above the level 

 of the sand, their usual position (p. 426). That these reactions were 

 not the result of the light that fell into the dish from above is seen 

 from the fact that similar reactions were obtained from animals that 

 were liberated in a covered glass dish of sea water containing a layer of 

 sand between one and two centimeters thick and illuminated by a mir- 

 ror from below only. Under these circumstances the amphioxus came 

 to rest in the sand, but in such positions that in many cases their bodies 

 were exposed to light through the glass bottom of the dish, though their 

 anterior ends projected into the darkness above the sand. Thus it is 

 evident that they did not enter the sand to escape the light. Moreover, 

 amphioxus will rest quietly, much as when it is in sand, provided all 

 but its anterior end is covered with small fragments of glass. Through 

 this covering the light may pass to the animal, and apparently this does 

 not disturb it, for its quiescence seems to depend merely upon the 

 contact of its body with the particles of glass. I therefore believe that 

 amphioxus is thigmotropic. 



The movements by which amphioxus buries itself are not without 

 interest. As a rule the animal dropped passively through the sea 

 water to the sand below. When it came in contact with the sand, it 

 sometimes gave a sudden spring and disappeared below the surface. 

 More frequently, however, it straightened out upon the sand, as noted 

 by Miiller ('44, p. 84) and by Willey ('94, p. 10), and later, particularly 

 if it was moved by a current, it would arch and disappear below the 

 surface, as described by Rice ("80, p. 8). Its disappearance into the 

 sand was so quickly accomplished that it was impossible for me to as- 

 certain by direct observation whether the animal entered the sand with 

 the anterior end first or the tail first. Steiner ('86, p. 497) maintains 

 that the anterior end of the animal enters the sand first, and that it 

 may continue to burrow through the sand till this end emerges. He 



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