122 THE ZOOLOGIST. 



outside small box altogether into a corner of the cage. (Subse- 

 quently moved inside again.) In December and January, great 

 gnawings at woodwork of cage, and evident anxiety to get out. 

 Jan. 28th, another mouse killed by accident, leaving only three, 

 one male and two females. February was a comparatively quiet 

 month, mice becoming reconciled to cage. 



Three young ones were born on the 7th or 8th of March, the 

 mother being about five months and a half old. 



Calling the females A and B, the following table shows their 

 productive powers :- 



Judging from this table, the period of gestation seems to be 

 about three weeks. I have added a mark of doubt to A in the 

 last two instances, because being absent from home in Iceland 

 during June and part of July, I am unable to say whether A or B 

 was the mother of the mice born on June 12th and July 9th, but 

 that A was the mother I have little doubt. 



On my return from Iceland I found it impossible to recognise 

 my pets ; some were dead, others had escaped, and many of the 

 young were now as large as their parents. I cannot therefore 

 give any accurate notes subsequently, but the above table shows 

 what two female Long-tailed Field Mice are capable of in less 

 than five months ; and had not one of the females (I have sup- 

 posed B) escaped early in June the number of young would have 

 been still larger. During April we had twelve to twenty mice, 

 young and old, in the nest ; they all slept together, and it was 

 certainly a curious sight to see father, mothers, and children of all 

 ages and sizes in the nest, the young of different ages suckling 

 the same mother at the same time, and the mothers appearing to 

 suckle each other's young indiscriminately. They also seemed 

 to have no cessation of suckling; but on this point I will not 



