BREEDING HABITS OF ALBINO RAT 293 



The present paper has as its object the filling in, as far as 

 possible, of such stages as have not previously been described, 

 and the presentation of evidence regarding the time relations 

 in the development of individual eggs. The authors' thanks 

 are due to Prof. W. R. Coe for the use of the notes and drawings 

 of the eggs of the brown rat, and to Dr. T. B. Osborn of the 

 Connecticut Agricultural Experiment Station for the designs of 

 the cages used and for the animals with which the work was 

 started. 



BREEDING HABITS 



About 150 albino rats were under observation at different 

 times during the investigation. One' large cage was used for all 

 rats not at the time under special care. For individuals two 

 types of cages were employed, one, a cylindrical cage of wire 

 netting of sufficient size to accommodate two rats at a time, 

 and the other a much larger, rectangular cage of galvanized iron, 

 with wire netting only on the front and bottom. This second 

 type of cage was designed primarily as a breeding cage and was 

 large enough to house a mother rat and a litter of the largest 

 size until the latter were sexually mature. 



The food of the animals consisted of oats, corn, wheat, sun- 

 flower seeds, and dog-biscuit, together with bits of lettuce, string 

 beans, bread, and various kinds of cooked meat and fish. 



All cages were kept as clean as possible, but except when 

 absolutely necessary litters less than two weeks old were never 

 disturbed. At the times when we were inspecting them the rats 

 were encouraged to come out of their cages and run about the 

 room, and to this faixdliarity with us as well as to the additional 

 exercise thus secured we attribute much of our success in rear- 

 ing large litters without their being maimed or eaten by the 

 parents. 



Usually females were isolated in breeding cages as soon as 

 they were seen to be pregnant, but in the few instances when 

 males were left with such females until several days after the 

 birth of the litter no mortalitv occurred. This fact leads us to 



