110 THE ZOOLOGIST. 



the two races inter-breeding much under natural conditions. 

 The presence of Mice of an intermediate type (but such are 

 far from common), and the fact that I once found a typical 

 sylvaticus and a typical flavicollis living in the same nest in a 

 bee-hive — the little wretcheB had destroyed all the bees ! — 

 suggests that such crossings may occasionally take place ; but 

 I have also known Yellow-necks kill and eat the smaller Mice. 

 In January, 1914, I put seven Mice in one large cage. There 

 were four Yellow-necks, one Mouse of the intermediate type, 

 and two Common Long-tails. At first, as far as I could see, 

 they agreed quite happily, but on the second day I found the 

 Mouse of intermediate type dead and partly eaten. In two 

 days another one was killed. This was a small male that was 

 really rather of the intermediate type than a true Yellow-neck. 

 Then I investigated the matter. I found a fine old male 

 flavicollis with two females in a nice nest in one corner of the 

 cage and the sylvaticus pair at the opposite end, where they also 

 had made a nest. One of them had been bitten, and I removed 

 them and put them by themselves. Thinking the matter over, 

 I thought it might only be a case of a big powerful male 

 bullying the smaller ones ; so I decided to see what would 

 happen to a Short-tailed Meadow- Vole, for if it were only a 

 case of the males fighting they would surely not interfere with 

 a Mouse of a different species. I put the Vole into the Yellow- 

 neck's cage and awaited events. It ran about and nibbled at 

 the grass which I had provided for it, and soon one of the big 

 Mice peeped out of the domed nest. Its great beady eyes looked 

 this way and that, and its nose worked in a manner that showed 

 it smelt a new-comer. Very cautiously it stepped out, paused 

 and sniffed, then with a bound it attacked the Vole. There was 

 much squeaking and scuffling, and the poor little stranger was 

 chased round the cage, and I have no doubt would have been 

 killed had I not interfered and rescued it ; but it had already 

 been bitten in the leg. 



It seems that the Yellowed-necked Mice are intolerant of the 

 presence of Mice of other species, and even object to nearly 

 allied forms. Surely this trait in the character of the race will 

 be a powerful factor in bringing about segregation ? And that 

 flavicollis and sylvaticus are an example of how two varieties 



