438 Joiininl of Comparative Neurology and PsycJwlogy. 



During the day Palacnion and Hippolytc are (^uiet and sluggish, but in 

 the evening they become very active and restless, many throwing 

 themselves out of the shallow pans in which they are kept. Hence 

 the authors think that these animals should be considered nocturnal. 

 Experiments on phototropic reactions (going toward or away from the 

 light) showed that the animals ex})enmented on formed a series, Pal- 

 acmon being negatively i)hototi'opic (light-shunning), Hippolyte positive 

 (light-seeking), and Macivmysis negati\e on a white ground hut posi- 

 tive on a black ground. The zoeae of PaIac))tou, however, are posi- 

 tive, and if given a choice of ground select the white. The adult 

 PalacDioii and Macivmysis choose the black, whWc Hippolyfc in all stages 

 prefers the white. A test was made to determine whether the posi- 

 tively thigmotrojMe Palaciiioii could be driven from the bottom of a 

 bottle, whose upper portion was darkened, l)y its negative photolrop- 

 ism. As long as there was nothing in the upi)er part of the bottle to 

 cling to, the animal returned to the bottom after a short swim above. 

 When an inclineil stick was |)lacc(l in the ujjper end of tlie bottle, 

 Palacmon remained clinging to it in the shadow. 



The effect of light upon pigment migration is discussed in great 

 detail. The effect of light stimulation was found to be in part tlirect, 

 and in part indirect, i. e. through the eyes and the nervous system. 

 The indirect response is the most important for color display, but its 

 action is slower, so that the direct response often gets a start, and then 

 is checked by the indirect. The direct response is determined not by 

 the background but by the incident light, whereas the indirect re- 

 sponse is determined by the l)ackground entirely, a white ground caus- 

 ing contraction of pigments, and a black ground expansion. "There 

 is a close agreement between the phototropic reaction and the i)igment- 

 movement reaction ; both dei)end on the eye and both are determined 

 by 'background' ". 



"A monochromatic light in conjunction with a scattering (white) 

 or absorbing (black) background, produces the same ultimate effect on 

 pigment movement as does a white light in conjunction with the same 

 background. The fact of background must be taken into con- 

 sideration in all experiments on phototropisni." 



In conclusion let it l)e said that the work is well su})i)lied with 

 summaries, an appendix of i 7 tables, a bibliogra])hy of 62 numbers 

 and seven s])lendid plates. j. carleiox hkll. 



