and Laboratory Methods. 1183 



intensity remains the same, (c.) It was found that at evening the prawns change 

 regularly and uniformly from their diurnal color to a deep, transparent blue. 

 This blue color passes away in the morning and the diurnal color of the previous 

 day reappears. This nocturnal change with its associated diurnal recovery is a 

 periodic phenomenon. The nocturnal blue appears at certain intervals even if 

 the illumination is kept constant for several days at a time, and on the other 

 hand the recovery of the diurnal color occurs regularly in specimens kept in the 

 dark during similar long periods. Blinded prawns exhibit the same periodicity. 

 The general physiological condition of the animals is very different during the 

 night and the day. 



Other experiments showed that the condition of the chromatophores at any 

 time is the result of impulses passing to them from the central nervous system. 

 Color changes can be induced by a variety of stimuli such as temperature, 

 chemicals, electricity, etc., which affect the nervous system. Removal of the 

 eyes causes a change in the impulses going to the central nervous system 

 and hence a change in the color. The nocturnal condition is a result of a 

 periodicity in the action of the nervous system. The relation of the nocturnal 

 color of these prawns to the color of deep sea animals is discussed. 



This paper is an important contribution to the physiology of coloration. 

 Unfortunately in the space of a brief review it has been impossible to do more 

 than mention some of the most significant points in the great amount of interesting 

 detail presented in the work. The admirably executed plates are a feature of 

 the paper. The experimental methods described are numerous and valuable. 



R. p. 



Yerkes, R. M. Reactions of Entomostraca to -j^j^g purposes of the investigation were 

 Stimulation by Light. II. Reactions of *^ "^ ° 



Daphnia and Cypris. Amer. Jour. Physiol. 4 : to determine the relation between the 

 405-422, 1900. j-^^g q£ movement and the intensity of 



light ; to determine whether there is a reversal of the phototactic reaction of 

 Daphnia and Cypris under certain conditions ; and finally to study the effect of 

 other stimuli on the light reactions. In regard to the first point it was found 

 that Daphnia moved only slightly faster as the intensity of the light increased, 

 while Cypris showed a still less definite relation between rate and intensity than 

 Daphnia. No very conclusive results came from the experiments devised to test 

 the question of reversal of phototaxis from positive to negative and vice versa. 

 Daphnia usually gives a positive reponse which could be maintained indefinitely 

 by changing the direction of the light. In some cases it was possible to change 

 this positive reaction into a weak negative one by taking the anirhals up in a 

 pipette as described by Towle (Amer. /our. Physiol. 3: 345-365), but this 

 result was not constant. The reverse change from negative to positive was not 

 obtained, owing apparently to lack of negatively phototactic animals on which to 

 experiment. In the case of Cypris, negative animals were made positive by 

 contact with the sides of the pipette. Raising the temperature does not affect 

 the phototaxis of these crustaceans. Sudden illumination of the animals from 

 above in such a way that the directive influence of the light is excluded does not 

 cause any change in the direction of swimming. In one set of experiments some 

 strong HCl was put into the trough at the end nearest the source of light. The 



