Acknowledgments. 13 



In a study of this kind, in which new characters are appearing from 

 time to time, there are always some on hand which have not been 

 fully studied in respect to linkage. This is true of several in the 

 present case. These have been included for the sake of completeness, 

 although in some instances little can be given beyond the description 

 of the character and its mode of origin. 



The method of detecting linkage among non-sex-linked characters, 

 and thus of assorting them into linkage groups, has been by means 

 of F2 counts, and back-crosses of heterozygous males. In the 

 earlier experiments each new character was tested with representa- 

 tives of all known linkage groups, and most of the characters have 

 been so tested; but more recently the tests have been discontinued 

 as soon as a character was found to be linked to one of the test char- 

 acters. The data from these purely test experiments are not included, 

 except in the cases showing linkage. 



In considering each linkage group, the data from the test experi- 

 ments are all given first; then follow the experiments from which 

 crossover values are taken. This method of treatment facilitates 

 examination of the linkage data. 



The order of the genes on the maps has been determined in the 

 usual manner, mainly by means of three-point crosses. In the latter 

 case the smallest cross-over class has been assumed to represent the 

 double cross-overs and the order has been arranged accordingly. 

 In a few cases the order has been determined by ''locating" a gene 

 with reference to two others independently. 



The records of matings given in the text and tables refer to the 

 original laboratory notes. Those not prefixed, or prefixed by V, L, 

 or M are records of C. W. Metz, those prefixed by E are records of 

 E. D. Mason, and those prefixed by P are records of M. S. Moses. 



ACKNOWLEDGMENTS. 



We are indebted to Professor T. H. Morgan and to Doctors A. H. 

 Sturtevant, C. B. Bridges, and D. E. Lancefield for the loan of 

 specimens and for information concerning mutant characters in 

 other species of Drosophila, and also for suggestions as to their 

 possible relationships to characters in D. virilis. Dr. Bridges has 

 furnished information on D. melanog aster, Dr. Sturtevant on melano- 

 gaster and simulans, and Dr. Lancefield on obscura. Our indebted- 

 ness is particularly great to Dr. Sturtevant, whose interest and 

 cooperation have added materially to the progress of the work from 

 its inception. We likewise acknowledge with gratitude the assistance 

 of the following persons, who made the drawings and photographs 

 for the accompanying figures: Miss E. M. Wallace, figures 5 and 12 

 and plate 1; Miss G. Ruth Lincks, figures 4 and 6; Miss E. M. Lord, 

 plates 2 to 4. 



