430 PROCEEDINGS OF THE AMERICAN ACADEMY. 



more energy than at the normal temperature. Finally they dropped 

 quietly to the bottom. 



At 20° C. they swam very energetically and near the top of the 

 water, but finally dropped to the bottom ; subsequently, on being 

 touched with a rod, they swam, but not so energetically as at the 

 normal temperature. 



At 15° C. they swam vigorously, but soon dropped to the bottom. 



At 10° C. they passed into the water without swimming, dropped to 

 the bottom, and remained quietly there. 



At 5° C. they behaved as at 10° C. After remaining on the bottom 

 at 5° C. for five minutes, they were removed to water of ordinary tem- 

 perature, where their reactions seemed to be entirely normal. 



Five active amphioxus were then dropped into water at 4° C, and 

 after half an hour they were tested and all found to be dead. The 

 temperature of the water at the end of half an hour had fallen to 

 2.5° C. This experiment was several times repeated, and always with 

 the result that death followed exposure to extreme cold for half an 

 hour or so. 



Cold water from 25° C. to 15° C is certainly stimulating to amphi- 

 oxus. At 10° C. and lower no response is given, but death may 

 intervene, particularly at lower temperatures, from unknown causes. 



All attempts at local stimulation with cold water were entirely 

 unsuccessful. Water at 15° C, when applied as a current to the 

 anterior end, tail, or trunk, was without effect, though, as already 

 mentioned, immersion in water at this temperature called forth vigor- 

 ous swimming. A current of water at 2° C, when applied locally to 

 the anterior end, tail, or trunk, gave rise, as might have been 

 expected, to no reaction. 



The reactions to cold water, when they occurred, were quite as quick 

 as those to warm water, and must therefore have been the result of 

 a very superficial stimulation ; but whether this was a stimulation of 

 the whole outer surface, or of a special part of it, or of some special 

 region hke the entrance to the mouth, I am unable to say. 



The fact that amphioxus swims away from any source of considerable 

 heat places it among negatively thermotropic animals. That it can 

 be stimulated to active, non- directive swimming by both heat and 

 cold shows it to be thermokinetic. That it should be stimulated by 

 cold, but not influenced in a directive way by this stimulus as it is 

 by heat, favors the view that it possesses, like some higher vertebrates, 

 separate receptors for heat and for cold. 



