466 THE LANCELETS— CEPHALOCHORDA 



come out from the spinal cord and in the way the ganglion- 

 cells are disposed at and in their roots, and the segments show 

 a relative independence in locomotion, which reminds us of 

 what is seen when certain worms break into pieces. " A short 

 piece of the tail-end can swim well and behaves much as a 

 whole animal does ; and this for many days together. To il- 

 lustrate by a complex movement, normal animals in a shallow 

 dish persistently put their heads up over the edge of the dish 

 and then by swimming round the dish and pushing against the 

 edge succeed in wriggling over, if the edge is not too high. 

 The isolated tail makes the same persistent and apparently 

 purposeful efforts when the dish is nearly full of water. When 

 an animal is so macerated that all the tissues except the noto- 

 chord are gone from the middle of the body, the two parts 

 perform typical swimming movements but each with an inde- 

 pendent rhythm. This retention of the power of coordinated 

 movement by a few isolated segments is perhaps connected 

 with the large number of cutaneous fibres which have a short 

 course in the spinal cord. This makes it possible for the 

 muscles to be reflexly controlled by stimuli received at the 

 surface of the body in the same or adjacent segments." (J. B. 

 Johnston, 1905, p. 124). 



We owe to Professor G. H. Parker a very valuable study 1 

 of the sensory reactions of Amphioxus, and we propose to give 

 a summary of the chief results. Professor Parker's general 

 idea in his research was to discover whether Lancelets were not 

 primitive in activities, as well as in structure and development. 

 " As the structure of Amphioxus throws light on the complex 

 organization of the Vertebrates, so its activities may give some 

 indication of the way in which the more complex functions of 

 these animals have come into being." 



{a) Sensitiveness to Light. — Lancelets are very slightly 

 sensitive to light, for although several observers have de- 

 scribed the wild excitement when a lighted candle is taken into 

 a dark room where the Lancelets are being kept, a more careful 

 scrutiny has shown that when the light first falls on the dish 

 a few move slightly and jostle others, and then in an instant 

 the whole assembly is in wild confusion. " It would seem that, 



1 "The Sensory Reactions of Amphioxus," Pvoc. Amer. Acad., xliii. (1908), 

 pp. 415-55- 



