428 PROCEEDINGS OF THE AMERICAN ACADEMY. 



3. Heat. 



The reactions of ampliioxus to heat have been scarcely more than 

 touched upon by the numerous investigators who have studied the re- 

 actions and habits of this animal. As has already been pointed out, the 

 opinion of Rohon ('82, p. 38) and of Kohl ('90, p. 185), that the light 

 reactions of amphioxus are really reactions to radiant heat, is erroneous ; 

 moreover it is not to be expected that animals like amphioxus, which 

 live always under some depth of water, would have any special organs 

 for the reception of radiant heat, since such heat penetrates water only 

 a centimeter or two and hence would almost never reach these forms. 

 The kind of heat that is a factor in the environment of amphioxus is 

 the molecular vibration such as we recognize in the temperature of 

 water, and this certainly has a distinctly circumscribing influence on 

 the lancelets. 



In testing the effect of heat on amphioxus, the temperature of the 

 water in which they were living in the Flatts Inlet, 31° C. (July, 1905), 

 was taken as the normal, and two series of experiments were conducted, 

 one at temperatures above this and another at temperatures below it. 



When lancelets were transferred from sea water at 31° C to sea water 

 at 35° C, they responded by darting about several times and then sink- 

 ing quietly in the characteristic way to the bottom of the dish. Their 

 subsequent reactions were essentially normal. 



When transferred to sea water at 37° C, they made several quick 

 darts, and finally fell quietly to the bottom, where they rested. When 

 under these circumstances dilute acid was applied to them, they were 

 found still to be actively responsive. 



When transferred to water at 40° C, they made one or two sudden 

 plunges, after which they dropped to the bottom, while their semi- 

 transparent substance gradually whitened. When touched with dilute 

 acid, the animals quivered slightly, but did not react otherwise. In a 

 short time they were dead. 



At 42° C. the animals darted once or twice, whitened quickly, and 

 dropped to the bottom dead. Bert ('69, p. 21) states that water at 

 41° C. kills amphioxus in two minutes. 



At 45° C. no locomotor response at all was given, and the animals 

 began to whiten at once ; they were apparently dead before they 

 reached the bottom of the dish. 



It is plain from these records that heat has at least two influences 

 on amphioxus. It stimulates them to momentarily vigorous locomo- 

 tion, and it also brings about death by the coagulation (whitening) of 

 certain materials in their living substance. The coagulation begins 



