58 
ZOOLOGY: A. W. L. BRAY 
mosome. I am inclined to think there are more than two. It seems prob- 
able that one of these factors was present at the beginning of selection and 
that the others occurred as mutations during the course of the experiment. 
The complete data and analysis will be given in the final paper. 
THE REACTIONS OF THE MELANOPHORES OF AMIURUS TO 
LIGHT AND TO ADRENALIN 
By A. W. L. Bray 
Zoological Laboratory, Museum of Comparative Zoology, Harvard College* 
Communicated by G. H. Parker, January 8, 1918 
The following is a brief summary of results obtained in experiments to test 
the reactions of the melanophores in the skin of Amiurus to light and to ad- 
renalin. The fishes tested were kept under as normal conditions as possible 
and no fish was used until it had become accustomed to its laboratory sur- 
roundings and to handling. 
The melanophores of Amiurus contract under the influence of light of ordi- 
nary intensity and expand in the dark. Fish kept in white porcelain aquaria 
contract the melanophores to a much greater extent than do animals kept 
in black lined aquaria under similar conditions of overhead illumination. 
When the eyes are removed from normal healthy animals the latter remain 
dark under all light conditions. There are considerable differences in indi- 
viduals with respect to the power of contraction of the melanophores. Some 
fishes become extremely light owing to complete contraction of the pigment 
cells; others, under similar conditions, never become so light. This cannot 
be explained entirely by the relative numbers of melanophores per unit area 
of body surface, as was shown by several counts. It may be due, possibly, 
to differences in nervous excitability. 
If some ' sensitive' individuals are raised to a high pitch of nervous irrita- 
bility, the melanophores are contracted to the maximum extent, and remain 
in this condition for a protracted period, even when the fishes are placed in 
the dark. One such fish was kept in the dark for three weeks and no expan- 
sion was observed in the melanophores. These cells appeared to be in a 
condition comparable to tetanus. 
When such an 'excited' animal, with melanophores contracted, is ether- 
ized, the pigment cells expand and the fish becomes dark. On coming out 
of the ether, the melanophores contract slightly, but if the fish is now placed 
in the dark, the pigment cells gradually assume the expanded condition. If, 
however, the eyes are removed whilst the fish is under ether, there is no 
return to the contracted condition when the animal is subsequently kept in 
the light. The fact that there was no return to the contracted condition 
