102 Referate. 



that from which our common domestic mice are derived. In the light of 

 this question it is important to note that quite recently Droogleever 

 Fortuyn 1) gave his reasons for considering the waltzing mice as derived 

 from Mi/s ^im^iicri. a central Asian species with a short tail, with a lesser 

 number of rings, like waltzers have. 



Artificial waltzers were made for Morgan, by injection of acetyl atoxyl 

 and matings of such mice, which waltz as well as ordinary waltzers were 

 made, showing that the permanent modification produced by the drug was 

 not inherited, just as of course was expected. 



Morgan next puts the question whether black and chocolate are different 

 pigments or only stages in the development of the same pigment. He 

 suggests that black pigment is produced by a further development of the 

 same chemical process that produced chocolate. In the absence of direct 

 experimental insight into the nature of this chemical process, I do not 

 think the question as put by Morgan is as yet answerable, but I fail to 

 see how the ultimate answer to this question should be able to affect our 

 conception of the difference between black and chocolate as produced by 

 the presence or absence of one definite genetic factor. It is not impossible 

 that Morgan thinks, that on the "presence and absence" scheme, it is 

 believed that in cases like this the difference between the two colours is 

 caused by the presence or absence of black pigment and it can not enough 

 been emphasized that the things which we believe to be either present or 

 absent in the germ are those things which by their cooperation to the 

 development, no matter how indirectly, influence this in a certain specific 

 way, thus causing under certain circumstances a difference in qualities, 

 "characters" between an individual in whose germ they are present and 

 one in whose germ they were not. 



The "presence and absence" scheme tries to explain certain phenomena 

 in terms of presence and absence of genetic factors, and by no means 

 presence or absence of characters, or pigments or organs. 



From the plate given in the paper of a "dilute gray" (dilute agouti 

 or dilute cinnamon agouti) I would judge the animal to be dilute cinnamon 

 agouti. 



A second sport noted by Morgan is a mauve-coloured one. I think 

 it well possible from the description, that these mice are such as have lost 

 the factor B, such as I have called yellow agoutis. It will be extremely 

 interesting to hear about breeding experiments with these mice, as, for as 

 far as I know, the only recessive yellow mice, which are fully analogous to 

 yellow rabbits and cavies were bred by me. If these sports are of the 

 same kind as mine, a mating of one to black or chocolate should give 

 agouti F], which in the first case would give four kinds of Fo, agouti, 

 black, yellow agouti and tortoise in ratio 9:3:3:1, in the second case 

 eight kinds, agouti, cinnamon, yellow agouti, black, chocolate, tortoise, clear 

 orange and orange, in proportions of 27:9:9:9:3:3:3:1. 



If this be so, Morgan will be able to produce, as I did, yellow mice 

 equivalent to yellow rabbits and red guinea pigs. For such animals differ 

 from such of other colours through the absence of one genetic factor, 

 whereas the yellow mice studied hitherto by Morgan have this factor, and 

 another one, not present in non-yellow mice these yellow mice and red 

 cavies are therefore by no means equivalent as M. assumes. 



1) A. B. Droogleever Fortuyn, De cytoarchitectonie der groote hersenschors 

 van eenige knaagdieren. Dissertatie. Oct. 191 1. Amsterdam. 



