382 



GENES MODIFYING NOTCH. 



morphs ; the former will be expected to kill any male that gets it, the 

 latter should give normal males. Hence a few males are expected 

 under these circumstances — the number depending on the '' distance" 

 apart of the lethals involved. Two cases in which lethals appeared 

 are given below: 



The question of origin of the new lethal that appeared is not with- 

 out interest. All of the eggs must contain it in the X chromosome 

 allelomorphic to the one carrying Notch; hence it must have arisen 

 in a single primordial cell from which all the cells of the ovary have 

 come, or else it must have been present in the single spermatozoon that 

 fertilized the egg from which the female in question developed. Since 

 the new lethal is here contained in the eosin-ruby-bearing chromosome 

 it is shown to have come from the male, and it seems probable here 

 (although not ej^licitly shown since the behavior of the sisters is not 

 recorded in the table), from a single one of his spermatozoa, viz, the 

 one that fertilized the female under discussion. If subsequent work 

 proves that when this kind of lethal arises the sisters of the lethal- 

 bearing female are not lethal-bearing, it follows that the mutation took 

 place in the last stages of the formation of the spermatozoon and per- 

 haps at the time of maturation (which would give two such sperm), or 

 even later after the sperm itself is formed. 



The complete proof that the high sex-ratios here found are due to a 

 lethal can only be established by breeding the daughters and by show- 

 ing, as has been done in other such cases of high sex-ratios, that two 

 lethals were present. As this point has been sufficiently established 

 in other instances, it was not thought worth while to test it out here. 



OTHER CHARACTERS THAT LOOK SOMETHING LIKE NOTCH. 



In the course of the selection experiment a number of other charac- 

 ters have come up, and, since they involved the ends of the wings, might 

 be taken by a neophyte as modifications of Notch or even perhaps as 

 " caused " by the selection of Notch. Two points may be noticed here : 

 first, that three of these mutations at least were in the direction 

 opposite to the direction of selection, and second, that they might 

 act as modifiers of the character selected, even although they hap- 

 pened to be mutations already known. 



Cut is a mutant with outer and inner edge of wing cut off, leaving 

 a pointed end (fig. 102). It is a well-recognized character and appeared 

 in a male in one of the selected cultures, viz, SS AAA 874626114. 



