SEXUAL CHARACTERISTICS OF THELIA 559 
perfect female coloration (fig. 12), while many show merely a 
medium condition (fig. 11). In slightly modified males the 
yellow hypodermal pigment of the vitta becomes fainter and less 
abundant, and melanie spots appear in the cuticula of the vitta 
(fig. 10). In individuals showing greater assumption of female 
coloration the melanin loses its uniform distribution outside the 
vitta, becomes restricted more and more to the punctures, and 
encroaches still farther upon the vitta. Yellow-green hypo- 
dermal pigment forms and shows through the cuticula no longer 
impregnated with melanin (fig. 11). Finally, in completely 
altered males, the punctures alone are brown (fig. 12) and the 
hypodermal pigment is exactly like that of the normal female in 
color and distribution. These changes are summarized in figures 
13 and 14. Figure 13 represents ten vittae seen in reflected 
light, and figure 14, the same in transmitted light. Yellow pig- 
ment appears light in figure 13, and dark in figure 14, since it 
absorbs the actinic rays of the transmitted light. Melanin is 
dark in both figures. The clear punctures of the male vitta are 
light in transmitted light (fig. 14, a). Vitta ain both figures is 
that of a normal male; vitta 7, that of a normal female. Vittae 
b to h, inclusive, are parasitized males and illustrate the gradual 
loss of yellow accompanied by the coming in of melanin in the 
punctures. In g and h complete assumption of female colora- 
tion has taken place. Vitta 7 is that of a parasitized female. 
It shows no tendency toward the assumption of male pigmenta- 
tion. At most parasitized females show smaller punctures with 
restricted melanic pigment and a thinner and weaker cuticula. 
This is doubtlessly due to an interference with the normal nutri- 
tion of the hypodermal cells which produce the chitin, as a sim- 
ilar condition may often be noted in parasitized males. In these 
cases there may be an actual scarcity of the necessary materials 
for chitin and pigment production, caused by the presence of the 
parasites. 
It must be clearly borne in mind that no modification in the 
integument can be effected by the parasites after the host has 
become an adult. The degree of change is, therefore, dependent 
upon the activity of the parasites previous to the final molt of 
