A brief account of the development of the dancer given by Zoth (31 p. 149)
adds nothing of importance to the description given by Alexander and
Kreidl. As my own observations disagree with their accounts in certain
respects, I shall now give, in the form of a diary, a description of the
important changes observed from day to day in a normal litter. The litter
which I have selected as typical of the course of development in the
dancer grew rapidly under favorable conditions. I have observed many
litters which passed through the various stages of development mentioned
in this description anywhere from a day to a week later. This was usually
due to some such obviously unfavorable condition as too little food or
slight digestive or bowel troubles. According to the nature of the
conditions of growth the eyes of the dancer open anywhere from the
fourteenth to the twentieth day. This statement may serve to indicate the
degree of variability as to the time at which a given stage of development
is reached by different litters.

On July 14, 1906, No. 151 (female) and No. 152 (male) were mated, and on
August 3 a litter of six was born to them. The course of the development
of this litter during the first three weeks was as follows:--

_First day_ The skin is pink and hairless, several vibrissae are visible
on the nose and lips, but there is no definite response when they are
touched. The mice are both blind and deaf, but they are able to squeak
vigorously. The mother was not seen to dance or eat during the day.

_Second day_. There is a very noticeable increase in size. The vibrissae
are longer, but touching them still fails to cause a reaction. No hairs
are visible on the body. The mother danced rapidly for periods of a minute
several times while the record was being made. She ate very little to-day.