588 



THE AM ERIC AX NATURALIST 



[Vol. L 



the only ones suitable for study, it has been necessary to 

 breed the various species in confinement in order to de- 

 termine their chromosome groups. As a result only 

 about half of those collected have been studied cyto- 

 logically. Other determinations will be reported in the 

 future as they are obtained. 



The material has been secured from four regions, New- 

 York, Massachusetts, Alabama and Cuba, with the excep- 

 tion of one species (not found in these localities) from 

 California and Oregon. 1 Fourteen of the twenty-nine 

 species are undescribed and are here given the manu- 

 script names of Dr. A. H. Sturtevant. 2 Descriptions of 

 them are in press. 



Most of the chromosome descriptions in the present 

 paper are taken from pedigree material, either first or 

 second generation from wild flies,- and the results have 

 been checked up in such a way as to make it very improb- 

 able that serious errors have crept in. As mentioned in 

 previous papers the chromosomes of these flies stand out 

 with diagrammatic clearness when favorable figures are 

 secured ; and since they are uniformly arranged in pairs 

 and are often of various sizes they offer admirable ma- 

 terial for a comparative study. This makes it possible 

 to classify the members of each chromosome group ac- 

 cording to their size and shape, and to assort the groups 

 into definite types according to their configuration. 



Desceiption of Types 

 The terminology used in describing the chromosomes 

 will be the same as that used in my previous paper ('14). 



