COLOR AND THE COLOR SENSE. 331 



III. 



As spiders further advance in age and make their successive moults, 

 various color changes may be noted. Immediately after moulting the 

 color is always lighter, which is probably due to the fact that 

 . ^ the harder skin just cast off prevented the passage of light 

 ences. through the tissues. The new skin is thinner and more trans- 

 lucent. Moulting produces changes in color patterns of a de- 

 cided kind, at least in certain species. 



Phidippus rufus when mature is a dark red spider, the male consider- 

 ably brighter than his consort. When about one-seventh grown and after 

 the third or fourth moult, the young are dark brown with light yellow 

 legs. Some moults later they are reddish, with narrow, oblique, whitish 

 bars on the sides of the abdomen, and two dark bands on the dorsum, on 

 each of which is a row of white dots. The appearance of the spider 

 changes but little during the next four moults, but after the last, the 

 tenth, both male and female become mature, and acquire the adult color. 

 The appearance of the female after the fifth moult is similar to that of 

 many other females in the genus. 1 



The female of Phidippus johnsonii has the abdomen red and black 

 with a white base and some white dots, while the male abdomen is bright 

 vermilion red, with sometimes a white band at the base. The young of 

 both sexes resemble the mother, until the last moult, when the males as- 

 sume their bright livery. 2 



In old age the color changes are often quite decided. In some, as Epeira 

 trifolium and Epeira thaddeus, the changes give added brilliancy to the 

 color at certain parts of the body. Some of the color changes 

 ? rs of Trifolium are remarkably beautiful, and the same is true of 

 Thaddeus. But advanced age, as a rule, brings darker colors. 

 Orange and brown then have a ruddier hue ; yellows darken into orange 

 and brown. Sometimes the yellow patterns are entirely lost, and the spi- 

 der becomes dark, almost black. There is a grizzled appearance about the 

 animal in this stage which reminds one of vertebrate animals at the cor- 

 responding period. These last named changes are manifest in the female 

 spider after the final deposit of eggs. 



In gravid females changes of color are sometimes noticeable. Some of 

 the bright colors upon Trifolium and Thaddeus are doubtless due to this 

 condition. However, other and perhaps most species during ges- 

 tation have a lighter color, which may be the result of mechan- 

 ical changes in structure. The skin becomes distended and more transpa- 

 rent, the pigment is thereby distributed, and thus centres of color are 

 broken up and the coloring matter diffused. Not only the skin, but other 



1 Peckhams, Sexual Selection, page 25. 2 Idem, page 17. 



