102 Hagedoorn. 



iiials. No long series of generations in cultivation has made these birds 

 any tamer or more suited to life in captivity. They are no more 

 domestic birds than those, which are hatched from eggs gathered in 

 the jungle. 



The domestic rabbits however, or the laboratory rats, often differ 

 from wild rabbits or wild rats in colour or shape, and they always differ 

 considerably in disposition. The wild European rabbit, which is alleged 

 to be the main •progenitor of the domestic rabbits, is as wild after a 

 few generations in captivity as any wildcaught one. It can not be made 

 to breed in hutches with any regularity. The wild sewerrat, Mus 

 norvegicus, which certainly enters largely into the ancestry of our 

 laboratory animals, is very unreliable and vicious, even atter generations 

 of cagebreeding. Is it possible to account for the tameness of our small 

 rodents, by assuming that they originated as a result of crossing with 

 some other wild species? We will see in the body of this paper that 

 such is actually the case. In the domestic rabbit, we know that several 

 North-American cottontails are very closely related and may have fur- 

 nished material for hybridization. The European hare almost certainly 

 produces fertile hybrids' with domestic rabbits. The laboratory rat, 

 although it interbreeds with Mus norvegicus and produces fertile hybrids, 

 can not be said to be a variety of this rat. In its pure state, as it 

 comes from the Orient, it is considerably smaller, the ears are larger, 

 the eyes larger and fuller, the coat is shorter, sparser and glossier, the 

 tail naked and the skull is approximately intermediate in character 

 between that of Mus nor,vegicus and rats of the rattus group. 



The domestic cavy differs very much from any wild species, in 

 size, in shape, but also in disposition. Experiments of Blaringhem and 

 Detlefsen have sufficiently shown, that different wild species may be 

 taken into account as progenitors of our tame guineapigs. 



So far, no fertile hybrids between species of mice have been produced, 

 unless the oriental domestic mouse is taken to be specifically distinct 

 from the European housemouse. But here again, the difference in dis- 

 position between the tame laboratory mice and wild housemice is very 

 striking. Occasional albino housemice have been caught and bred by 

 us for several generations of breeding in cages as wildcaught stock. If 

 it has been crossed however, in other words, if the albinism is due to 

 admixture of escaped mice, selection will soon tone down the wildness 

 of such a strain. 



