CILIARY ACTIVITY 43 



phase and the black background expanded phase are produced 

 no matter whether the Hght intensity is high or low, variable 

 or constant. 



The chromatophores of isolated strips of the integument 

 of the shrimp react to bright light by expansion. This suggests 

 that there is a direct response of the chromatophores in 

 Crustacea. After amputation of the eyes in Macromysis or 

 Palaemon the chromatophore pigments, instead of assuming 

 the contracted phase, expand when the anim^al is placed on a 

 light-reflecting bottom ; in fact, in the case of Palaemon, a 

 deep chocolate colour even darker than the normal expanded 

 condition associated in the intact animal with a black back- 

 ground is produced. But the contracted phase characteristic 

 of the nocturnal state occurs at night in Hippolyte even after 

 the eyes have been removed. These data permit the inference 

 that the nocturnal- diurnal rhythm depends on the direct 

 reactivity of the chromatophores to the intensity of illumination, 

 and the white and black background responses are determined 

 by events conditioned by photic stimulation of the organs of 

 vision. 



The supposition that the eye exerts its influence upon 

 colour response in virtue of the intensity of illumination alone 

 is adequate to explain the peculiar reversal of response in seeing 

 and blinded salamander larvse as described by Babak and 

 Laurens. But it offers no explanation of the fact that a bright 

 white background which scatters light produces in the intact 

 shrimp a response similar to darkness, while a dull black back- 

 ground which reduces the intensity of illumination acts in the 

 direction of intensifying the diurnal state. Some other factor 

 besides intensity of illumination is involved, and the 

 transcending importance of this factor is clearly seen in experi- 

 ments which are described as follows in Keeble and Gamble's 

 own words : — 



" To show how, compared with this influence of background, 

 that of light intensity is of small importance, we mention the 

 following experiment which we have often performed with 

 Hippolyte and Macromysis. We take with us on a collecting 

 expedition four jars, two of glass wrapped round with black 



