244 CASWELL GRAVE 



duce locomotion, but throw the body into vibration with the 

 appearance of oscillatory movement the same as that seen when 

 locomotion in a normal tadpole is prevented by confining it 

 between slide and cover. 



The rotary method of locomotion in the ascidian tadpole may 

 be accidental and have no special significance, but it is of some 

 interest to find its method of swimming is that characteristic of 

 the early larvae of invertebrates in general and not like that 

 of vertebrates. 



REACTIONS TO LIGHT 



When colonies of Amaroucium are placed in a rectangular 

 glass jar lined except for one side with unglazed black paper 

 and the jar is so placed that light enters the water through the 

 uncovered side, the tadpole larvae, as they are liberated, swim 

 through the water first in an undulatory course obliquely upward 

 toward the light, then up along the side of the glass to the 

 surface of the water where they dodge back and forth for a few 

 seconds attempting to proceed toward the source of the light. 

 They then leave the illuminated side and swim into the less 

 illuminated parts of the jar, where they remain, alternately 

 active and quiescent, throughout their free-swimming period. 



Castle^ noted that "Ciona and Amaroucium tadpoles avoid 

 the light while that of Botryllus swims toward light." He 

 failed to observe the Amaroucium tadpole during the brief 

 interval when, on escaping from the parent colony, it shows a 

 positive light reaction. 



Occasionally a tadpole, in its initial excursion toward the 

 light, will turn in its course and swim away before it has reached 

 the lighted side of the jar. That is, the period of positive reac- 

 tion to light in some tadpoles is remarkably short, but is appar- 

 ently never entirely absent. 



Tadpoles do not swim in a straight course either toward the 

 source', of light, during the brief period when they react posi- 

 tively to it, or away from its source during their longer period of 

 negative response, but depart from a straight line in all direc- 

 tions and, at times, they travel in circles and curves of con- 



