

HELIOTBOPIC TEANSFOEMATION 113 



The starfish poisoned with strychnine upon sudden 

 touch withdraws all the tube feet, so that it can be moved 

 about like an inert object. For this purpose 1 or 2 c.c. o' 

 a 0.5 per cent, solution of strychnine sulfate were injected 

 into a starfish of medium size. 



If the stretching out of the tube feet is due to an in- 

 crease in the tone of the ring muscles (and a decrease 

 in the tension of the longitudinal muscles) the drawing 

 in is due to an increase in the tone of the longitudinal 

 muscles of the tube feet. We therefore see that the same 

 " stimulus, " namely, a sudden touch, which causes one 

 set of muscles to contract in a normal animal causes the 

 antagonists of these muscles to contract in an animal 

 poisoned with strychnine. We shall see that a number of 

 cases of reversal of heliotropism may well find their 

 explanation on this basis. On the other hand, the phe- 

 nomena of solarization known in photography indicate 

 that the sign of heliotropic response may also be changed 

 by an excessive action of light on the photochemical sub- 

 stance. This effect, of course, may in the last analysis 

 also result in an influence upon the central nervous system, 

 such as that brought about by strychnine in Moore 's ex- 

 periment. We will now consider some cases more in 

 detail. 



The writer found 296 that certain fresh water crusta- 

 ceans, namely Californian species of Daphnia, copepods, 

 and Gammarus when indifferent to light can be made 

 intensely positively heliotropic by adding some acid to the 

 fresh water, especially the weak acid C0 2 . When car- 

 bonated water (or beer) to the extent of about 5 or 10 c.c. 

 is slowly and carefully added to 50 c.c. of fresh water 

 containing these Daphnia,, the animals will become in- 

 tensely positive and will collect in a dense cluster on the 



8 



