J18 Hagedoorn. 



into the fieldrat produced our novelties. The houserat is never found 

 far away from buildings, in our garden in Buiteuzorg they would hardly 

 venture out upon a trellis to attack our passionfruit. The treerat is 

 more enterprising. It enters houses, where it fights the houserat and 

 occasionally mates with it and it makes foraging trips in the fields. 

 This is an additional reason, why it is much more proliable, that the 

 unknown ancestor of our aberrant fieldrats was a rat of this species 

 than a houserat. 



It is very improbable, that whatever cross produced the novelties, 

 should have given variation in colour only. The only other character 

 examined is size. The albino female was very small and so were some 

 of her grandchildren. Even after many generations there was a very 

 noticeable variability in size between rats of one litter in this series. 

 Numbers are altogether too small to find out anything definite about 

 a character, so influenced by nou- genetic developmental factors, but 

 from the fact that the very small rats seem to form a minority, 

 it appears probable that tliis small size is recessive compared to 

 normal size. 



In disposition our rats differ markedly from purebred fieldrats, 

 which difference may be looked upon as further proof of their origin 

 by crossing. Purebred fieldrats of the Sumatra strain were as wild in 

 the fourth cagebred generation as handreared wildcaught young. It 

 proved wholly impossible to tame these rats, even if they were raised 

 by tame fostermothers. By handling a young rat daily, it is possible 

 in some species to keep it wholly tame. — This is true for Mus norregicus, 

 for the Javanese houserat and the treerat and for the yellow and agouti 

 rats of our hybrid series. 



Fieldrats however, and the miniature houserat, JUus concolor, can 

 not be tamed, no matter at what low age their education is taken in 

 hand. Young rats of these species will" try to run from the hand before 

 their eyes are open, and they will bite if restrained. We have con- 

 siderable experience with small nervous mammals, but we never soicceeded 

 in getting a rat of either species tame. Rats of the albino series 

 however are tamed with relative ease. All our albinos could be safely 

 handled. Even the rats which have never been handled, are consider- 

 ably less shy than fieldrats of pure breeding, and more active in 

 daytime. In this they resemble houserats or treerats. An unconscious 

 selection, the fact that only those pairs had offspring which would breed 

 in our comparatively small cages, assuredly helped to make these rats 



