Specifs ciosscs in Rats. ]13 



Ainoug the rats from Buitenzorg which reached us safely iu 

 California, was a pair of fieldrats, which one of us had caught iu a 

 licefield in South East Sumatra. In all external characters these rats 

 were like the .Javanese fieldrats, witli the exception of a slightly different 

 taillength. 



Cream. 



The first charaoter to he treated of is the cream colour of one 

 of the three females. The female was mated to the male fieldrat from 

 Sumatra and gave one litter of 7 darkbellied agoutis. The colour of 

 the unterside of these hj'brids, like that of all fieldrats is pale grey, 

 with slaty undercolour, we call it dark to distinguish it from the white 

 of the belly of some other rats in the fieldrat series presently to be 

 desci'ibed. 



From two paii-s of these Fi animals, 28 young were obtained, of 

 which 23 agouti, and 5 creamcoloured. No new colours or other 

 novelties were obtained from this cross. 



This same cream female, while nursing the first litter, forced her 

 way out of the cage and mated to a darkbellied yellow male of our 

 houserat-treerat series. From this mating she had .3 young, all males, 

 which died when a month old. These were all darkbellied agouti. This 

 shows, that the cream colour in this fieldrat .was not due to the same 

 genotypic aberration, which produced yellow colour in the houserat 

 series. We will therefore name it the gene K. 



Pale agouti. 



The pale female, mated to the male from Sumatra had 9 young, 

 all agouti with the normal belly colour of fieldrats. 



From one pair of these Fi animals we obtained three litters of 

 F2 rats. This gave us 16 agoutis, 5 pales, and 1 albino. The in- 

 heritance of the pale agouti colour showed the difference between agouti 

 and pale agouti to be due to one single gene, which we may call L. 

 The occurrance of albinism in this F^ generation requires some comment. 

 If the cream female had been heterozygous for a gene necessary for 

 pigmentation, albinism could be expected to crop out from mating of 

 two heterozygous Fi young. But in that case there would have been 

 one albino in four, whereas there was only one among twentytwo. This 

 ratio is much closer to one in sixteen, and for this reason the possi- 

 bility that in this case albinism was due to a simultaneous absence of 



Induktive Abstammungs- und Vererbungslehre. XXIX. 8 



