1901.] Allen, Opossums of the Genus Didelphis. I7 1 



Moult, and Variation with Age and Season. In young 

 specimens the first pelage consists of very short woolly hair, at 

 first almost wholly blackish. As the hair increases in length it 

 becomes lighter at the base, and later nearly pure white for about 

 two thirds of its length. When the animal is a few weeks old the 

 long coarse overhair begins to appear, being white or black ac- 

 cording to the phase. By the time the animal is one fifth grown 

 its pelage is similar to that of the adult and there is no further 

 change except what results from fading and wear. 



The present series of specimens does not afford satisfactory 

 material for a complete study of the moult. From October till 

 February the pelage is generally full and long. In March it 

 often shows signs of wear, and by April becomes exceedingly 

 worn and ragged. At the same time new hair can be seen coming 

 in, at first in patches where the old pelage has been removed by 

 accident. April and May specimens generally show new hair 

 coming in, but whether a full summer dress is acquired remains 

 uncertain. Through individual idiosyncrasy specimens occur 

 sporadically from January to July that are very much worn, but 

 in general there appears to be a renewal of the coat in April and 

 May. August to September specimens also show new growth of 

 hair, which continues to come in, at least in certain specimens, 

 till late in October. By the end of October the full winter coat 

 has generally been attained. It is interesting to note that the 

 underfur in the new fresh coat is often nearly clear white, this 

 condition occurring at widely separated localities. Later the 

 underfur commonly takes on a slightly yellowish cast, which be- 

 comes more pronounced as the season advances, so that speci- 

 mens in worn condition often have the underfur decidedly 

 yellowish white, and the white overhair is often soiled or stained 

 dingy yellowish. Quite a number of specimens, from various and 

 widely separated localities, have the underfur of the head, neck, 

 and shoulders quite deep buff, and the rest of the underfur more 

 buffy than usual, due apparently to adventitious staining. 



Dichromatism. The large Mexican Opossums of the Didelphis 

 marsupialis group are, like those of the D. karkinophaga group, 

 subject to dichromatism, they presenting a gray phase and a 

 black phase similar to the gray and black phases so well known 

 to occur in various species of Squirrels. While the two phases 



