468 THE LANCELETS— CEPHALOCHORDA 



that Amphioxus remains buried in the sand during the day 

 (except perhaps for its anterior end), but that it leads a more 

 active life at night. Parker's observations on Branchiostoma 

 caribbceum showed no evidence of nocturnal activities. 



(b) Sensitiveness to the temperature of the water. — Professor 

 Parker, has shown that heat has at least two influences on Lance- 

 lets. It stimulates them to momentarily vigorous locomotion, 

 and, in excess, it brings about death by coagulation, which be- 

 gins at about 40° C. They swim away from any source of 

 considerable heat just as they do from bright sunshine, so that, 

 if we say the same thing in technical words, they are negatively 

 thermotropic and negatively phototropic. They are stimulated 

 to active swimming by water colder than 31° C, and they 

 are killed by prolonged exposure to water of 4 C, or lower. 

 "That Ampihoxus should be stimulated by cold, but not in- 

 fluenced in a directive way by this stimulus as it is by heat, 

 favours the view that it possesses, like some higher vertebrates, 

 separate receptors for heat and for cold." 



Amphioxus is very sensitive to mechanical stimulus, the 

 most sensitive parts being the oral hood and the buccal 

 cirri. It will also respond to sound-waves. Professor Parker 

 says : "If a glass vessel that contains resting Amphioxus 

 partly buried in the sand is gently tapped on the side, the 

 animals, as Rice observed long ago, usually withdraw tempor- 

 arily below the sand, or at least move their cirri in a way that 

 resembles winking. That this is not due to the vibration of 

 particles of sand against their bodies is seen from the fact that 

 at least the reaction of the cirri can be called forth from 

 animals that are resting on a bed of cotton wool in a glass 

 vessel of sea-water when the walls of the vessel are tapped. 

 . . . It is very probable that these reactions to sound depend 

 upon the stimulation of some part of the tactile mechanism, 

 for in the first place Amphioxus has no special organ that can 

 serve it as an ear, and secondly, many sound-vibrations can be 

 sensed through our tactile organs as well as our ears." 



Amphioxus rests quietly when its body is in contact with 

 particles. These are normally sand particles, but particles of 

 glass will serve ! This curious experiment corroborates what is 

 otherwise clear, that the Lancelets do not enter the sand to 

 escape the light. 



