28 The Dancing Mouse 



have changed rapidly. In one of the females, which seems 

 to be a little in advance of the others in development, certain 

 peculiarities of behavior appeared to-day. She jumped and 

 squeaked sharply when touched and sprang, out of my hand 

 when I attempted to take her up. This is in marked contrast 

 with her behavior previously. 



Fifteenth day. The eyes are partly opened. All of the 

 members of the litter came out of the nest box this morning 

 and ran around the cage, dancing frequently and trying to 

 eat with the mother. Three out of the five gave auditory 

 reactions on first being stimulated ; none of them responded 

 to repetitions of the stimulus. All appeared to be less sensi- 

 tive to sounds than yesterday. The quick, nervous, jerky 

 movements are very noticeable. 



Sixteenth day. The eyes of all five are fully opened. They 

 dance vigorously and are outside the nest much of the time. 



Seventeenth day. No reactions to sound could be detected 

 to-day. The sense of sight gives evidence of being well 

 developed. The nervous jumping movements persist. 



Eighteenth day. The young mice continue to suck, al- 

 though they eat of the food which is given to the mother. 

 They are now able to take care of themselves. 



Nineteenth day. There are no noteworthy changes except 

 increase in size and strength. 



Twentieth day. No auditory reactions were obtained to- 

 day, but other forms of stimulation brought about unmis- 

 takable responses. 



Twenty-first day. They are now about half grown and there 

 is no other change of special interest to be recorded. Growth 

 continues for several weeks. The statement made by Alexan- 

 der and Kreidl to the effect that the dancer is almost full grown 

 by the thirty-first day of life is false. At that age they may 

 be sexually mature, but usually they are far from full grown. 



