1888.] NATURAL SCIENCES OF PHILADELPHIA. 173 



3 In old age the color changes are very decided in almost all 

 species. In some, as Eperia trifollum and Epeira thaddeus, the 

 changes give added brilliancy to the color at certain parts of the 

 bod3\ Some of the color changes oftrifolium are very beautiful and 

 the same is true of thaddeus. 



But advanced age, as a rule, makes the colors darker. Orange 

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

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

 spider becomes very dark, almost black. There is a grizzled appear- 

 ance about the animal in this stage which reminds one of the corre- 

 sponding condition of man and lower vertebrate animals. These 

 last named changes are manifest in the spider after the final deposit 

 of eggs. 



4 In gravid females the changes of color are often very decided. 

 Some of the bright colors upon trijol'ium and thaddeus are doubtless 

 •due to this condition. Most spiders during gestation have a lighter 

 color, which may be the result of mechanical changes in structure. 

 The skin becomes distended and more transparent, the pigment is 

 thereby distributed, and thus centres of color are broken up and the 

 color matter diffused. Not only the skin, but other parts of the ab- 

 domen are distended during gestation, and this distension produces 

 changes in the color of the animal by modifying in some way the 

 various secretions from the liver and other organs. 



5 The little pits or dark spots u|)on the dorsum of the abdomen 

 which mark the attachment of the muscles Avithin, appeared to him 

 to be centres for aggregation of coloring material. At least the 

 dorsal patterns seem to be grouped in some regular way around 

 these muscular attachments. Thus the action of the muscles on the 

 skin and chitinous shell or walls serves to compel certain aggrega- 

 tions along the lines of use, that form these colors and patterns. 

 It might be important in this connection to consider what is the 

 ordinary effect of muscular action upon the distribution of pigment 

 in the human system or with vertebrate animals ? * 



The color rings or annuli around the joints of the limbs of spiders 

 may also be produced by action of the muscles. It is noticeable 

 that the tendency of these darker and more vivid colors is towards 

 the ends of the joints, as though by the outward action of the mus- 

 cles the pigment were forced mechanically or otherwise attracted 

 toward these points. 



In the cephalthorax may be noted the same tendency of color to 

 group itself around the points of muscular attachment, particularly 



* After the remarks here recorded, Dr. Nolan, the Secretary, called attention to 

 the fact that he then had in hand for publication a paper by Dr. Harrison Allen, 

 on " The Distribution of the Color Marks of the Mammalia." This paper has 

 now appeared, and is a most valuable and interesting one. (See Proceed. Acad. Nat. 

 Sci. Phila., 1888, pp. 85-105). The following sentence is quoted therefrom as 

 bearing upon the above suggestion : " The stripes and spots on the limbs and the 

 dapple-marks on the trunk, as well as some ot the broader sheets of color, a]ipear 

 to be related to the intervals between the muscle-masses or to the extent of skin 

 surfaces which correspond to muscles." p. 100. 



