34 PECKHAM. [Vol. 1. 



is but little difference among the various species. Passing over 

 the many and great differences of structure in the last or tarsal 

 joint of the male palpus, which are primary sexual characters, 

 we find, in this organ, many curious modifications of form and 

 of ornamentation the only use of which is to please the 

 female.^ 



In some species they are greatly elongated (Lagnm longi'- 

 manus) ; in others there are curious enlargements and apophy- 

 ses on one or more of the joints {Plexippus puet-perus); but the 

 most frequent and by far the most striking form of decoration 

 is a covering of long white or yellowish hairs which gives them 

 a plume-like appearance (Pensacola signata). 



In many spiders the sexes differ not only in the beautiful 

 plumose palpi of the male, but also in the locomotive organs. 

 The legs of the first pair are lengthened, in many males, and 

 the several joints are enlarged and brilliantly colored, or fur- 

 nished with long hairs or iridescent scale-like sette. In no 

 family of spiders does sexual selection seem to have been more 

 effective than in the Attidas. Many of the species, as we have 

 seen, are furnished with remarkable falces, elaborate head or- 

 naments and plume-like palpi, and we have now to give an ac- 

 count of a further modification which has apparently been 

 gained for the sake of ornament, or possibly through the sham 

 battles between the males. 



In an ant-like species, Synageles picata, the female has legs 

 of the ordinary form ; but in the male the tibia of the first leg 

 is enlarged and flattened, and the anterior face of the enlarge- 

 ment is of a brilliant, steel-blue metallic color, as glossy as the 

 breast of certain pigeons. In PMlseus meiallescens, from Aus- 

 tralia, tlie legs of the first pair in the male are 11 mm. long, 

 while those of the female are only 9 mm.; those of the male 

 are of a very brilliant steel-blue color, and are ornamented 

 with rings, spots and fringes of short, scale-like hairs, and of 



1 Koch and Keyserling in Arachniden AustroUen!^ describe in the family 

 Attidce thirty-tour males having well developed fringes or tufts of hair on the palpi, 

 while there are only tive females so ornamented, and several of these to only a mod- 

 erate extent. 



