102 INFLUENCE OP HORMONES 



showed that in the same species the corpora lutea 

 persisted not only during the whole of pregnancy, 

 which Professor J. P. Hill ^ estimates at a little over 

 eight days, but during the greater part of the period 

 of lactation, which according to the same authority 

 is about four months. In the specimens of Dasyurus 

 described by O'Donoghue, in which the milk glands 

 developed after ovulation without ensuing preg- 

 nancy, normally developed corpora lutea were 

 present in the ovary. Of the ^yq females which he 

 mentions, the first three, one with unfertilised ova 

 in the uteri, two five and six days after heat, could 

 not have been pregnant, but the other two killed 

 eighteen and twenty-one days after heat might, since 

 pregnancy lasts only eight days, have been pregnant, 

 the young having died at parturition or before. To 

 make certain on this point it would have been neces- 

 sary to examine the ovaries and milk glands of females 

 which had been kept separate from a male the whole 

 time. There is no doubt, however, about the de- 

 velopment of the milk glands in the first three 

 specimens, which were certainly not pregnant. 



It is difficult to reconcile entirely the evidence 

 described by O'Donoghue from Dasyurus, with that 

 obtained from higher Mammals, although on the 

 whole there is reason to conclude that the corpora 

 lutea have an important influence on the develop- 

 ment of the milk glands. According to Lane- 

 Claypon and Starling, if the ovaries and uteri are 

 removed from a pregnant rabbit before the fourteenth 

 day the development of the mammary gland ceases, 

 retrogression takes place, and no milk appears in the 

 gland. If, on the other hand, the operation be 



^ AnaL Anz., xviii., 1900. 



