ACTIVITIES OF THE AMAROUCIUM TADPOLE 251 



the physiological response to gravity, has been followed up with- 

 out result. The position of the statolith cell in the wall of the 

 sensory vesicle of tadpoles fixed and preserved late in their free- 

 swimming period is not observably different from that in tadpoles 

 preserved at the time of their liberation from the parent colony. 

 Neither is there any change in the relation of the sensory vesicle 

 as a whole to adjacent structures. Slight contractions in the body 

 wall may be observed during resting periods, but there is ap- 

 parently no observable shifting of structures within the body 

 until the free-swimming period is over and metamorphic changes 

 have set in. 



In the experiments made to demonstrate the existence of a 

 definite reaction to gravity, distinct from that to light, unusual 

 and abnormal light conditions were arranged and the results, 

 recorded in columns 1 to 6 of the table, seem to show that light 

 when reflected directly downward or upward through the column 

 of water in a cylinder, jacketed with black paper to prevent the 

 entrance of light from the side, has a very decided effect in 

 modifying the response of the tadpoles to gravity. 



In table 2, which follows, the results of these experiments are 

 given in the form of percentages of tadpoles found attached at 

 various levels in the cylinder. 



A comparison of these figures with those given in the text on 

 page 247 will show the extent to which the normal response to 

 gravity is modified in the presence of unusual light conditions. 



Not only do tadpoles vary greatly in the degree to which they 

 exhibit a positive response to gravity, about 5 per cent not show- 

 ing it at all, but the response is such that it may be more or less 

 suppressed by the stronger negative response to light. When 

 light from a north window was reflected upward through the 

 column of water, during the period when 77 per cent of the tad- 

 poles normally migrate to the bottom, the response to gravity 

 was inhibited in more than 58 per cent of the tadpoles, about 

 19 per cent only finding attachment to the bottom. An even 

 greater inhibition of the response took place when direct sunlight 

 was reflected upward, 11.7 per cent only having responded 

 definitely to gravity. 



