108 ANNALS NEW YORK ACADEMY OF SCIENCES 



come full grown. Several other mice in the same cage showed a similar 

 change, but none so great as this one. The others showed patches of 

 lighter color and these may disappear again after several months or new 

 patches may appear. Similar effects, though not so great, have also been 

 seen in the mainland forms kept under the same conditions and also in 

 some of the mice from Marthas Vineyard. Other species also kept in 

 confinement have shown similar lightening of the coat color. Osgood 4 

 states for Peromyscus leucopus noveborqcensis that the coat is being con- 

 tinually moulted or "changed," although it appears to be entirely renewed 

 only once a year. The changes in color that come and go are undoubtedly 

 connected with the partial moulting of the individual, and it seems rea- 

 sonable to suppose that they are expressions of the physiological condition 

 of the animal at the time of moult. 



The important question as to which factor or factors in the environment 

 is responsible for the changes in color here recorded can not, I regret, be 

 given. Light seems to be excluded, since the animals are crepuscular, and 

 the room in which they were kept was lighted by a window, so that in 

 this regard the conditions were not very different from those in nature. 

 Food or temperature or humidity might be supposed to be the factors 

 that are probably involved. The food was varied, but contained less 

 green food than the animals generally obtain. The temperature was 

 much higher on the average than that to which the animals are normally 

 exposed. The air of the attic was extremely dry, yet it is to be remem- 

 bered that this lighter-colored race has arisen on an island where the 

 moisture is extremely high, so that if there is any relation between the 

 color and the environment, we should expect dryness to produce the re- 

 verse effect. Until control experiments can be carried out, it will be best 

 not to assign the change to any one of these possible agents. 



How far these changes may be carried in later generations remains 

 also to be shown. It is, however, sufficiently obvious that, if changes as 

 great as these may take place, the results of crossing different species in 

 confinement must be carefully controlled by studies of the influences of 

 the confinement itself. 



General Conclusions 



the ticked or gray hair as a "unit character" 



Under the microscope, the hair of the common gray mouse is found to 

 contain three pigments, black at the base, yellow in the middle and brown 

 (or chocolate) at the tip. This banded condition is obviously like that 



* Revision of the mice of the American genus Peromyscus. North American Fauna, 

 No. 28. 1909. 



