No. 538] REPRODUCTION IN THE BROWN 11 A T 



length 52 mm. as compared with 41) mm. for the females. 

 They also weigh more, and by the end of the second 

 week are as much as two grams heavier. 



Very little change is noted in the appearance of the 

 young the first two days, save a gain in size and strength. 

 On the third day a change in color can be detected. The 

 flesh tint is being replaced by a darker hue with a de- 

 cided tinge of blue on the distal portion of the tail. 

 ( 'uriously enough, the tail is the first to show any marked 

 change of color. On the fourth day, the tail is still 

 darker and the flesh color of the dorsal parts has been 

 replaced by a gray with a touch of blue. Up to this time, 

 no hair is noticed except the vibrissas By the end of 

 the week the body is covered with a thin coat of very 

 fine hair, which gives a delicate bluish-brown color. The 

 coloring of the legs begin about this time with the palms 

 of the feet, the joints of the toes and legs turning a 

 bluish tint. The tail, in the meantime, has darkened al- 

 most to the base and the nose turned nearly black. On 

 the eighth or ninth day, the gray of the adult is noticed 

 on the back of the head and neck, and with this as a 

 center, it spreads until about the eighteenth day, when 

 the whole color is that of the adult with the exception 

 that it is darker and softer. 



The following is a diary of litter No. 18 for the first 

 twenty-five days. The weights given are the aver; 

 for the whole litter. 



Day Wt. Grams Notes 



1 6.1 Flesh color; blind; ears closed; helpless. 



2 6.4 Able to right themselves if turned over. 



