660 



The Common Mole. 



[Oct., 



pregnancy. If this holds good with regard to the mole, six weeks 

 rather than one month is nearer the actual period of gestation, 

 as some nests from which the writer has taken young had been 

 made about a month previously. 



The following evidence is sufficient to prove that the female 

 litters only once a year. 



Hundreds of dissections at all times of the year show that an 

 enormous development of testes, prostate and corpus spongiosum, 

 takes place in the male commencing late in January, and culmi- 

 nating about the end of March or the beginning of April, when 

 pairing takes place. These organs afterwards decrease in size, 

 until by the end of May they have become normal again. They 

 remain in this condition during the rest of the year. 



There is thus only one short "rutting" season, practically 

 confined to the latter part of March. April, and perhaps occa- 

 sionally the beginning of May, after which both sexes are com- 

 pletely exhausted. The earliest personal record the writer 

 possesses for a fcetal litter (which was within three or four days 

 of birth) is 13th April, and the latest date he has seen young 

 in the nest is on 25th June; these young moles were quite 

 ready to leave the nest. 



Thus, on the assumption that the period of gestation is four 

 weeks (it is probably rather more) it is evident that the female 

 would not have time to breed twice within the time mentioned 

 during which young are found, even, as is not the case, if she 

 were in condition to do so. Moreover, these limits of earliest 

 and latest births are not those of the same year or locality, so 

 they may be fairly curtailed, and a month of courtship may be 

 presumed to be the limit of the mole's capacity. 



The average number of young in a litter works out at rather 

 more than 3-5. The writer's personal records are as follows : — 



1 litter containing 1 young. 



4 litters containing 2 young. 



20 litters containing 3 young. 



31 litters containing 4 young. 



4 litters containing 5 young. 



1 litter containing 6 young. 



The writer selected one mole for measurement from each of 

 several litters, and others from the same nests at intervals, and 

 has prepared the following table of the rate of growth and con- 

 comitant personal appearance from the day of their birth to the 

 twenty-second day, when they are ready to leave the neat. The 

 measurements are in millimetres. 



