COLOR AND THE COLOR SENSE. 349 



indicate a segmentation. In other words, some writers are disposed to con- 

 sider tlie abdomen as segmented, and, in a rough way, the symmetrical 

 divisions in the pattern folium may be said to outline the articulations of 

 the segments. 



The cephalothorax is most frequently uniform in its color, commonly 

 with longitudinal stripes of different shade. It follows, in a general way, 

 the coloration of the legs, which it resembles in its chitinous 

 Cephalo- character, the entire fore part of the body having the hardness 

 and Lea-s ^^'^'^^^ ^^ characteristic of the enclosing walls of insects. The ab- 

 domen, on the contrary, is enclosed in a soft skin, a fact which 

 exposes it to injury, and causes its rapid decay after death, one of the 

 principal difficulties in the way of preserving specimens of spiders. On 

 the cephalothorax there are often several longitudinal bands, one on each 

 side, near and indeed quite surrounding the margin, and two drawn from 

 the suture of the caput backward. There is also frequently a band of 

 color in the median line from the middle of the eye space backward. The 

 legs are usually colored like the cephalothorax, and are generally uniform 

 in hue, except that at the joints there are rings of color usually darker 

 than the rest of the leg. The feet are nearly always black or blackish. 



In order to determine if possible the structural causes producing color 



in spiders, I made studies from a number of dissections of various species 



chosen with special regard to variety and brilliancy of colors. 



„ „ , Among these are Argyroepeira hortorum, Argiope argyraspis, Ar- 



giope cophinaria, Argiope argenteola, Epeira insularis, Gastera- 



cautha cancer, and Pliidippus morsitans. ' I do not speak of the results 



positively, for the studies are in a field where trained histologists alone 



are competent to decide. But I venture to give some indications of what 



appeared to me, in the hope that others may follow the jjath suggested, 



and reach positive determinations. 



The metallic white upon the cephalothorax of Argiope argyraspis is 

 produced chiefly by a vast number of white hairis. These are packed 



closely one upon another and reflect white light, the combined 

 Metallic . . o > 



„ reflections forming the metallic appearance of the object. The 



metallic hues of the abdomen of Argyraspis are produced in 

 part by closely thatched white hairs that reflect white light in the manner 

 of those upon tlie cephalothorax. The black transverse bands on the ab- 

 domen are produced by amorphous granules of black pigment just beneath 

 the skin, whicli thin out towards the margin of the band, becoming yellow 

 as they diminish. Tliere appears also to be a diffused yellow stain in the 

 chitine, and, in addition, white pigment bodies which re.semble the cliro- 

 matophores that give the color in frogs and lizards, for example. 



' I had purposed to include in this volume a plate of colored drawinj^s representing, in 

 a general way, the indications of these stuilies, but sundry (lisa|i|inintiiiciils and dcliiys ha\'e 

 compelled the postponement of this plate to the third volume. 



