REPRODUCTION IN THE BROWN RAT (MUS 

 NORWEOICUS) 

 NEWTON MILLER 

 Clark University, Worcester, Mass. 



In view of the fact that the brown rat is playing such 

 an important role in the economic field and the medical 

 world at the present time, it is of interest if not of prac- 

 tical value to know the details of its reproduction. The 

 life history of this species as lived in its natural envi- 

 ronment is as yet imperfectly known. It was to bridge 

 this deficiency in our knowledge that data were obtained 

 on a number of rats kept in the laboratory from No- 

 vember 5, 1909, to December 8, 1910. My results may be 

 much different from those of natural conditions, yet I 

 am convinced that the results obtained are not radically 

 different from what actually takes place in nature where 

 shelter is good and food abundant. 



Two sets of cages of four each were built. The first 

 consisted of revolving cages, a foot wide and eighteen 

 inches in diameter with nesting boxes, measuring 

 8x5x5 inches, suspended from the axles. These 

 cages were similar to those used by Slonaker. The sec- 

 ond set of cages were rectangular, measuring 24 X 24 X 8 

 inches. These were made of screening, three wires to 

 the inch. For the sake of cleanliness the cages were 

 suspended, as shown in Fig. 1. Newspapers were spread 

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