278 CARNEGIE INSTITUTION OF WASHINGTON. 



theory to account for the origin of gynandromorphs and mosaics has 

 been proposed (Carnegie Inst. Wash. Pub. No. 278). 



The origin of mutations is one of the most difficult and perplexing 

 problems engaging the attention of biologists. Our material is slowly 

 contributing toward the solution of this problem in several directions. 

 For example, the reappearances of certain ''recurrent" mutations is 

 being carefully watched and parallels between mutations in Drosophila 

 and those in other species are being followed out. Some indications of 

 the nature of the mutative process are also afforded by the numerous 

 cases of multiple allelomorphs and ''deficiencies." 



In the course of the work new openings are continually appearing, 

 some of which are as fruitful as the main lines of work engaging our 

 attention. For example, several ways in which chromosome groups 

 may undergo evolution have appeared; through "non-disjunction" 

 whole chromosomes may be added or lost; by "duplication" sections 

 of chromosomes may be added ; and by " deficiency " sections of chromo- 

 somes may be lost. 



The work on a hereditary tumor in Drosophila (lethal 7) has been 

 continued by Miss Stark. The first paper is now about to appear in 

 the Journal of Cancer, and a second is ready for the press. 



The possible influence of radium on the hereditary material of 

 Drosophila is undergoing further investigation. 



The high female ratios (excess of females) that occasionally appear 

 have been analyzed and found due to sex-linked lethals. A high male 

 ratio, that has recently appeared, promises to give a clue to the 

 solution of this problem also. 



A further attempt to cross species of Drosophila having different 

 groups of chromosomes has been made, especially by artificial impreg- 

 nation, but so far without success. 



During the past year approximately 40 new mutations have been 

 found, which have provided us with means of controlling the behavior 

 of several chromosome regions about which our knowledge was formerly 

 insufficient. Several of these mutations are of such a character that 

 they add greatly to our working material, enabling us to attack both old 

 and new problems with greater success. We are now in position to 

 supply to others not only the method but also the material for the 

 solution of questions that could not heretofore be handled by exact 

 methods. At more than thirty institutions teachers are using our 

 material for demonstration of the principles of heredity to students, and 

 many of them are conducting researches of their own on selection and 

 other phases of heredity. Some of these institutions are now secondary 

 centers of distribution, so that the material is rapidly becoming widely 

 used. The maintenance of this valuable stock is becoming something 

 of a burden at headquarters. 



