THE BREEDING 'HABITS, MATURATION OF EGGS 

 AND OVULATION OF THE ALBINO RAT 



W. B. KIRKHAM and H. S. BURR 



Sheffield Biological Laboratory, Yale University 



EIGHTEEN FIGURES 



INTRODUCTION 



The present work was started by the senior author under the 

 supervision of Professor W. R. Coe in the spring 1907, and in 

 1908 Professor Coe published in Science a brief statement of 

 what had been found. In the summer of 1911 the junior mem- 

 ber, Mr. Burr, took up the work. In the interim the literature 

 of the subject had been enriched by three papers, and since then 

 two additional ones have appeared. Lantz in 1910 contributed 

 to a United States government report, on the economic impor- 

 tance of the rat, a short paper on the natural history of the 

 animal. The author describes the different species of rats, their 

 distribution, and general habits, but pays little attention to the 

 details of their reproduction. 



Sobotta and Burckhard ('10) made a careful study of the 

 maturation and fertilization of the egg of the albino rat, and 

 they describe and figure the ovarian egg in the stages of the 

 first polar spindle, and first polar body with the second polar 

 spindle, and the tube egg in the stages of the second polar spin- 

 dle, fertilization, second polar body, and the pronuclei. Ovula- 

 tion is stated to occur independent of pairing within thirty-six 

 hours after the birth of a litter, and the eggs fertilized nine to 

 twelve hours after copulation. Sobotta and Burckhard found 

 the mature rat egg, in the ovary, to measure in preserved mate- 

 rial 0.06 to 0.065 mm. in diameter; practically the same as the 



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