_Group I_ _Group II_ _Group III_ _Group IV_ Abnormal Antlered Band Bent Bar Apterous Beaded Eyeless Bifid Arc Cream III Bow Balloon Deformed Cherry Black Dwarf Chrome Blistered Ebony Cleft Comma Giant Club Confluent Kidney Depressed Cream II Low crossing over Dot Curved Maroon Eosin Dachs Peach Facet Extra vein Pink Forked Fringed Rough Furrowed Jaunty Safranin Fused Limited Sepia Green Little crossover Sooty Jaunty Morula Spineless Lemon Olive Spread Lethals, 13 Plexus Trident Miniature Purple Truncate intensifier Notch Speck Whitehead Reduplicated Strap White ocelli Ruby Streak Rudimentary Trefoil Sable Truncate Shifted Vestigial Short Skee Spoon Spot Tan Truncate intensifier Vermilion White Yellow If the factors for these characters are carried by the chromosomes, then we should expect that those factors that are carried by the same chromosome would be inherited together, provided the chromosomes are definite structures in the cell. [Illustration: FIG. 52. Chromosomes (diploid) of D. ampelophila. The sex chromosomes are XX in the female and XY in the male. There are three other pairs of chromosomes.] In the chromosome group of Drosophila, (fig. 52) there are _four_ pairs of chromosomes, three of nearly the same size and one much smaller. Not only is there agreement between the number of hereditary groups and the number of the chromosomes, but even the size relations are the same, for there are three great groups of characters and three pairs of large chromosomes, and one small group of characters and one pair of small chromosomes. THE FOUR GREAT LINKAGE GROUPS OF DROSOPHILA AMPELOPHILA The following description of the characters of the wild fly may be useful in connection with the account of the modifications of these characters that appear in the mutants.