In the fourth figure (d) the mutant called dichaete is shown. It is characterized by the absence of two of the bristles on the thorax. Other bristles may also be absent, but not so constantly as the two just mentioned. Another effect of the same factor is the spread-out condition of the wings. The very dark eye color in this figure may be taken to indicate the presence of another factor, "sepia", which causes the eyes to assume a brown color that becomes black with age. Most of the other mutations in eye color that have occurred tend to give a lighter color: this one, which is also recessive, makes the eye darker. In the fifth figure (e) the color of the darkest fly is due to a factor called ebony, which is an allelomorph of sooty. In the sixth figure (f) the wings are beaded, i.e., the margin is defective at intervals, giving a beaded-like outline to the wings. This condition is very variable and much affected by other factors that influence the shape of the wings. The lighter eye color of the drawing may be taken to represent pink. In the seventh figure (g) the wings are curled up over the back. This is a recessive character. _Group IV_ Only two mutants have been obtained that do not belong to any of the preceding groups; these are put together in Group IV. It has been shown that they are linked to each other and the linkage is so close that it has thus far been impossible to obtain the dominant recessive. One of these mutants, called "eyeless" (fig. 56, a, a^1), is variable--the eyes are often entirely absent or represented by one or more groups of ommatidia. The outline of the original eye, so to speak, is strongly marked out and its area might be called a rudimentary organ, if such a statement has any meaning here. [Illustration: FIG. 56. Group IV. (See text.)] The other figure (b) represents "bent", so called from the shape of the wings. This mutant is likewise very variable, often indistinguishable from the wild type, yet when well developed strikingly different from any other mutant. This brief account of a few of the mutant races that can be most easily represented by uncolored figures will serve to show how all parts of the body may change, some of the changes being so slight that they would be overlooked except by an expert, others so great that in the character affected the flies depart far from the original species. _It is important to note that mutations in the first chromosome are not limited to any part of the body nor do they affect more frequently a particular part. The same statement holds equally for all of the other chromosomes. In fact, since each factor may affect visibly several parts of the body at the same time there are no grounds for expecting any special relation between a given chromosome and special regions of the body. It can not too insistently be urged that when we say a character is the product of a particular factor we mean no more than that it is the most conspicuous effect of the factor._