1 86 WILLIAM MORTON WHEELER. 



2. Mandibular Macrocheztez. — Both the dorsal and 'ventral 

 surfaces of the mandibles in many ants are clothed with short, 

 more or less projecting hairs, but the xerophilous species have 

 in addition on each of the jaws, a ventral series of long and 

 rather slender macrochaetae, which project downward and have 

 their tips curved inward and sometimes upward. These hairs are 

 longest on the bases and gradually become shorter towards the 

 tips of the mandibles. 



3. Mental Meter -ocheetee. — Some of the xerophilous species 

 have a tuft of macrochaetae on the postero-median portion of the 

 mentum, just in front of the anterior border of the gula. In one 

 genus {Ocymyrmex) they extend backward and downward, in 

 two others (Myrmecocystus, Melophorus) they project forward ; in 

 all cases their tips are turned forward or upward. 



4. Gular Macrocheetce. — In most of the xerophilous species, 

 these constitute the longest and most conspicuous hairs on the 

 whole body. They are inserted, often in an arcuate series, on the 

 posterior or lateral portions of the gula, are directed forward and 

 downward and are often curved upward at their tips. 1 



As these various series of hairs or bristles together constitute 

 a circumoral system, one is naturally inclined, on inquiring into 

 their function, to suspect that there may be a connection between 

 their development and some peculiarity in the feeding habits. It 

 is true, to be sure, that these habits are apt to be highly special- 

 ized in desert ants. The natural and primitive food of ants con- 

 sists of insects or the juices of plants, the latter collected either 

 directly from the floral and extrafloral nectaries or indirectly 

 after passing through the bodies of phytophthorous Homoptera 

 (Aphididae, Coccidae, Membracidae). But as insects and flowers 

 are rare for long periods of the year in arid regions, many xero- 



x The term gula is here used in the sense of Janet (" Recherches sur 1'Anatomie 

 de la Fourmi et Essai sur la Constitution Morphologique de la Tete de l'lnsecte," 

 Paris, G. Carre and C. Naud, 1900, 205 pp., 15 Pis.) as that portion of the cranial 

 capsule which arises from the fused labial, maxillary and mandibular segments. It 

 comprises the greater portion of the heavily chitinized antero-ventral integument of 

 the head, and is divided into two parts by a median longitudinal suture, the external 

 indication of the gular apodeme. In reality, as Janet has shown, the gular apodeme 

 represents the whole labial and maxillary and the mesial portion of the mandibular 

 segment of the cranium, so that the gula proper comprises not only the lateral, but 

 also the larger portion of the mandibular segment. 



