PARKER. — THE SENSORY REACTIONS OF AMPHIOXUS. 429 



apparently at about 40° C, and may be so rapid at 45° C. as to 

 prevent the characteristic locomotor reaction which occurs at lower 

 temperatures. 



Having ascertained something of the general effect of heat on amphi- 

 oxus, I next endeavored to determine what parts of its body were 

 sensitive to this stimulus. To this end I used a temperature 39° C, 

 a little lower than that which caused coagulation. I attempted to 

 apply this temperature locally by touching the animal in the region 

 to be tested with a sharply bent glass tube kept at the required 

 temperature by a rapid flow of hot water through it. The bent tube 

 thus heated was applied successively, but at considerable intervals, to 

 the anterior end, middle, and tail of several animals, and their reactions 

 recorded. As a check on this method the bent tube filled with water 

 at 31° C. was also applied to the animals, with the outcome that the 

 mechanical stimulation was found to be so considerable that the results 

 dependent upon temperature could not be rightly judged, and the 

 method was therefore necessarily abandoned. 



I next tried running a gentle stream of warm sea water on different 

 parts of the lancelet's body while it was resting in a dish of sea water 

 at 31° C, and I checked this method by using the same strength of 

 stream, but at the normal temperature. This procedure proved much 

 more satisfactory than the use of the bent tube, for the current of 

 water at the normal temperature seldom, if ever, gave rise to a re- 

 sponse, while that at 39° C. very generally did. 



"When the heated current was applied to the anterior end of a lance- 

 let, the animal very usually swam immediately backward a short dis- 

 tance. When it was applied to the tail, the animal often moved 

 forward. When it was applied to the middle of the body, the reaction 

 never was locomotor, but only a slight bending or jerking of the body, 

 and even this was apparent in only about one out of every ten trials. 



The reactions of amphioxus on being immersed in warm water or 

 touched by a current of warm water follow so quickly on the appli- 

 cation of the stimulus that I am convinced that stimulation takes 

 place on the surface of the animal, for there was scarcely time for the 

 heat to reach by conduction any relatively deep-lying part. I there- 

 fore conclude that heat is a sensory stimulus for amphioxus, and that 

 it is very probably effective for the whole outer surface of the animal, 

 the head being most sensitive to it, the tail less, and the middle 

 portion of the body least. 



In a second series of tests, water cooler than 31° C was used 

 with which to stimulate the amphioxus. When animals were trans- 

 ferred from water at 31° C. to water at 25° C, they swam about with 



