26 The Dancing Mouse 



the head is moved noticeably. The mother dances a great 

 deal and eats about twice as much as she did before the birth 

 of the litter. 



Sixth day. Certain regions of the skin, which were slightly 

 darker than the remainder on the fourth and fifth days, are 

 now almost black. It is evident that they are the regions 

 in which the black hair is to appear. The movement in 

 circles is much more definite to-day, although most of the 

 individuals are still too weak to stand on their feet steadily 

 for more than a few seconds at a time. Most of their time, 

 when they are first taken from the nest, is spent in trying to 

 maintain or regain an upright position. The hair is now 

 easily visible, and the skin begins to have a white appearance 

 as a result. 



Seventh day. Although they are strong enough to move 

 about the nest readily, none of the young has attempted to 

 leave the nest. They huddle together in the middle of it 

 for warmth. The epidermal scales, which have increased 

 in number since the third day, are dropping off rapidly. 

 Contact with the vibrissae or with the surface of the body 

 frequently calls forth a motor reaction, but neither light nor 

 sound produces any visible change in behavior. The black 

 and white regions of the skin are sufficiently definite now to 

 enable one to distinguish the various individuals by their 

 markings. The mother was seen to dance repeatedly to-day, 

 and she ate all the food that was given to her. 



Eighth day. A fold is plainly visible where later the 

 eyelids will separate. The black pigment in the skin has 

 increased markedly. 



Ninth day. The eyelids are taking form rapidly, but they 

 have not separated. The body is covered with a thick coat 

 of hair which is either pure white or black. Standing on the 

 four legs is still a difficult task. 



