OF WASHINGTON. 277 



The maxilla have, on account of their peculiarly modified form, 

 been variously understood by naturalists, and some of the writers 

 have considered them as an organ related to the lips or the tongue 

 (ligula, glossoide, languette, etc.)' 



The reason for considering this organ homologous with the 

 maxilla? of the Arachnida is that these organs appear in pairs, and 

 generally at the underside of the mandibles, which is exactly the 

 case here. The only instance where a ligula is present in the 

 Arachnida is in the higher Pedipalpi. the Amblypygi, where this 

 organ can be recognized by the pair of paraglossae inserted into 

 its apex, as is the case with Insecta. Koch and Pagenstecher have 

 also considered the lower part of the rostrum as maxillae. 



The maxillae appear here as one elongate, flat, and more or less 

 clavate piece, with a distinct middle line, indicating that it is 

 composed of two halves. They are generally about as long as 

 the mandibles when retracted ; sometimes a little longer, other 

 times slightly shorter ; their internal or upper surface is longitudi 

 nally excavated, thus forming the under half of the channel with 

 which the rostrum is provided. The free underside is covered 

 at the tip with radiating minute scales which give this part the 

 appearance of a rasp. Further down these scales assume a larger 

 size and form large lozenge-shaped plates w T ith their lower parts 

 drawn out into a tooth. This armature is strongest and most 

 prominent at the borders of the maxillae, where these teeth appear 

 as large hooks bent outward and backward. The arrangement 

 of this armature, the number of the plates, their form and the 

 area which they cover on the surface of the maxillae differ not 

 only in the sexes, but also in the genera and species, and furnish 

 very important criteria for classification. 



The palpi are situated on the anterior lateral angle of the basal 

 piece, on each side of and close to the rostrum ; they stand some 

 what sideways to the dorsal surface of the rest of the body and 

 are in most genera of the Antistomata about as long as the rostrum. 

 They have four joints, although some of the older writers could 

 only discover three joints. The palpi present in the different 

 genera a great variety of form and structure. In the family Ixo- 

 didae they are long and cylindrical, while in the Rhipistomidae they 

 are nearly as long as broad and more of a triangular shape. 

 These differentiations are made use of in the characterizations of 

 the genera. 



