330 CARNEGIE INSTITUTION OF WASHINGTON. 



the double recessive, bent eyeless, has been made on a large scale, 

 again without success, showing either that crossing-over does not occur, 

 or is very infrequent in this chromosome pair. However, the recent 

 discovery of fourth-chromosome dominants gives an opportunity of 

 renewing the attack, from a different angle. 



Since the last report, 28 or more mutants of a particular type have 

 been discovered in which dominance, minute bristles, and late hatching 

 are present and are correlated with several other peculkrities. Despite 

 their outward similarity in many details, it turns out that many of 

 these mutants have veiy different locations in the chromosomes. 



Two types of non-disjunction not yet described have been analyzed, 

 one in the XX YY female, and the other in XXX oogonia. The latter 

 furnishes an interpretation of a phenomenon called formerly "equa- 

 tional non-disjunction." Further studies of XX Y females have made 

 it probable that the Y does not influence crossing-over in the normal 

 tj^pe of non-disjunction, but does increase crossing-over in certain 

 types of "high non-disjunction." 



During the course of the year Professor O. L. Mohr, of the Uni- 

 versity of Christiania, Norway, has carried out further work with 

 Notch 8 (deficiency) and completed this work while with us during the 

 past summer, at Pacific Grove, California. His study has brought to 

 light some new and important characteristics of deficiency. 



Of the many attempts that have been made during the last few 

 years to hybridize different species of Drosophila, so far only one has 

 been successful, viz, D. melanogaster with D. simulans. As already 

 reported, the cross made one way {melanogaster 9 X simulans d^) gives 

 commonly females only; the reciprocal cross {simulans 9 X melanogas- 

 ter cf') gives males and occasional females. Since these hybrids are ster- 

 ile, it is not possible to continue the experiment further; but another 

 method of attack has been found, by which some of the mutant 

 characters in simulans have been proven to be identical with certain 

 ones in melanogaster. In order to do this it was first necessary to 

 obtain as many mutant types in simulans as possible. About 20 

 mutants have been obtained, of which 6 correspond to melanogaster 

 mutants already known. Since it has been shown that these mutant 

 characters are recessive when each mutant type is crossed to the wild 

 type of the other species, it follows that each wild type carries the 

 normal allelomorphs of the other species. And since the hybrids 

 between these recessive mutant races show the characteristics of the 

 two parents, we must regard the mutant genes as allelomorphic. This 

 means that the same gene has mutated in each species, and in the same 

 direction; and in at least 4 of the 6 cases the mutant characters appear 

 to be actually identical. Five of these corresponding genes of simulans 

 are in the X-chromosome. Their linkage relations have been studied, 

 and a comparison of the resulting map with that of 7nelanogaster 



