42 LESLIE B. AREY 



completion, the vigor of the muscular movements rapidly de- 

 creases and ends in complete collapse (Rice '80, p. 8; Parker '08, 

 p. 441). After cessation of movement the animal is carried on a 

 short distance by its own momentum and then sinks slowly to 

 the bottom. According to notes taken at the time, five of the 

 nine animals thus observed were judged chiefly by the finish 

 of their response; if a reversal occurred just previous to the ces- 

 sation of swimming, it is reasonable to expect that the nearly 

 exhausted animal would not reverse again but would continue 

 tail first mth the last feeble strokes which precede complete 

 exhaustion. 



When Amphioxus has been kept in the laboratory for a short 

 time the anterior half of many animals begins to turn pink and 

 in a few days that end may become decidedly colored. This is 

 presumably a manifestation of an approaching moribund con- 

 dition, although the reactions of the lancelets appear to be 

 practically normal. Observations of a number of Amphioxus 

 in this condition led to conclusions similar to those gained by the 

 study of artificially stained animals. 



Referring to the quotations above, it will be seen that the 

 views of Rice and of Steiner, although agreeing with mine in the 

 main, show some differences. Rice's statement that he never 

 saw an Amphioxus move 'tail-end foremost' is not only con- 

 trary to the results given in my tabulation, where nine out of 

 fifty observed animals were so oriented during normal swimming, 

 but is also not in accordance with Parker's ('08, p. 431; pp. 437- 

 440) experiments, in which resting animals stimulated mechanic- 

 ally or chemically on the anterior end or mid-body, responded 

 with a backward spring. Steiner's simple statement that 

 Amphioxus locomotes 'das Kopfende voran' is certainly" too 

 general and omits entirely any mention of the characteristic 

 backward movements just referred to in the criticism against 

 Rice. My own observations agree perfectly with Parker's, 

 to the effect that Amphioxus burrows in the sand tail first, but 

 his belief, obtained as an inference from this habit, that the 

 animal usually swims backward is directly opposed to the con- 

 clusion reached by me. 



