120 Hagedoorn. 



the median line of its head, whereas I have never yet seen or bred 

 a brown rat with white hair on the top of its head. 



As is well known, albino animals may either contain L or lack 

 it. In them it is impossible to see the difference between ll and ii 

 animals. It has been stated by Mudge that in albino young from 

 hooded rats, the peculiar coat-pattern may sometimes be seen when 

 the animal is young. I know this ghostpattern in rats, but I have 

 proved to my satisfaction that it stands in no relation whatever to 

 the colourpattern of the animal. This structurepattern is caused by 

 the circumstance that a young rat, when at an age of about two 

 months the moult begins, their new hair grows first on their flanks 

 and gradually extends upwards upon their backs. Those parts of the 

 coat where the old hair is falling out show the rosy skin through the 

 short hair, whereas those spots where the new, longer hair grows are 

 much whiter. This difference between long and short hair, makes 

 it possible to see the pattern on the coloured brothers of the albinos 

 having it, fully as well as on them. Thus it often happens that a 

 young rat with a black hood on a white coat, shows the structure- 

 pattern as well. An observation of this phantom-backstripe shows 

 further, that gradually it gets narrower and narrower, and finally 

 disappears. Counting together the litters from solid-coloured hetero- 

 zygous mice (Ll) mated to spotted ones (H) I find 247 animals, of 

 which 131 are spotted (U) and 116 solid-coloured (Li). The expected 

 ratio in this case is 123.5 • 123.5. As can be seen from the tables, 

 this factor l is transmitted independantly from the factors A, c, D 

 and G. 



These eleven factors are, as far as I know, all that have been 

 studied in the mouse. We have seen that, with the exception of E, 

 and I all these factors are also known in the cavy or the rabbit 

 or in both. 



We have seen that these factors in tlie same combinations cause 

 the same colours to appear in rabbits and cavies as in mice. The 

 circumstance that the rabbit, cavy and mouse are not bred in the 

 same colourvarieties is partly due to the fact that some factors, which 

 have been lost from the germ in some individuals in mice a long 

 time ago, have only recently been reported as lost from some cavies 

 or rabbits. So e. g. the factor c. Cavies without c have been known 

 only a few years, rabbits without c were until recently quite unknown 

 in England and America. The original individual without c has 

 probably been produced in the south of Holland. It is for this reason 



