THE AMEBIC AN NATUBALIST [Vol. LV 



In other cases the unilateral reaction of the melanophores was 

 less permanent, appearing as a transient phenomenon ; due per- 

 haps, to a differential reaction rate of the chromatophores of the 

 two sides. Two experiments^ illustrative of this point may be 



1. A live, normal, apparently healthy embryo of the lake white- 

 fish (Coregonus clupeaformis) , developed approximately to the 

 hatching stage, was found to have the dorsal melanophores con- 

 siderably "expanded" on the head, slightly expanded on the 

 body. Following the removal of the egg envelope, under ap- 

 proximately unchanged conditions, these color-cells "contracted" 

 in this order: (1) body, (2) left side of head, (3) right side of 

 head. Still under similar conditions, the cephalic melanophores 

 again expanded, those of the left side most widely. No further 

 change could then be induced, even by rather intense light-heat 

 stimulation, until the left eye was dissected out and the embryo 

 again held before the light. Reaction occurred at once only on 

 the left (now the blinded) side, the lateral melanophores con- 

 tracting more rapidly and more completely than the inner ones ; 

 as in the first instance, reaction followed (some time after the 

 removal of the stimulus) on the right side, the melanophores 

 contracting in the same order as on the left side. 



2. A similar embryo of the same species had the dorsal melano- 

 phores of the head well expanded when removed from its egg 

 envelope. The pigment granules of all melanophores on the right 

 side then rapidly migrated into the center of the cells, under 

 observation. No reaction occurred on the left side, even follow- 

 ing stimulation with a bright light, although this caused first a 

 partial contraction and then a re-expansion of the right chroma- 

 tophores. Reaction on both sides was finally accomplished by 

 sudden transfer of the eggs from water near room-temperature 

 (about 25°) to water at 1.7° C, but even in this case the contrac- 

 tion was more complete and rapid on the right than on the left 



