THE EXTERNAL STRUCTURE OF ANTS. 



21 



a! 



and specialized condition in the workers of more highly developed ants 

 like the Camponotinas. 



Emery starts with a primitive form like the male Streblognathus 

 a'tliiopicits (Rig.. 6). In this in- 

 sect the various elements or 

 sclerites of which the thorax is 

 composed are clearly delimited by 

 sutures. The prothorax is very 

 small and consists dorsally and 

 laterally almost entirely of the un- 

 paired pronotum, with a slender 

 ventral element, the prosternum, 

 to which the coxa of the fore-leg 

 is articulated. Owing to the de- 

 velopment of the wings, the meso- 

 and metathorax are much larger. 

 The former is especially well-de- 

 veloped, in correlation with the 

 larger size of the fore wings, and 

 comprises dorsally a large un- 

 paired, convex plate, the mesono- 

 tum ; ventrally on each side, and 

 articulated below with the coxa of 

 the middle leg, is the meso- 

 sternum, which also forms much 

 of the pleural wall of the thorax. 

 The space on each side between 



the mesonotum and the mesosternum is occupied by a pair of elements, 

 one of which, the mesepisternum, is ventral ; the other, the me^epi- 

 meron, dorsal. The fore-w r ing is articulated just above the mesepimeron 

 and below a small sclerite, which is behind the mesonotum and may be 

 called the mesoparapteron, or praescutellum. The insertion of the fore- 

 wing is covered by a small chitinous scale, the tegula. Viewed from 

 above the large mesonotum in some male ants presents a Y-shaped 

 groove, known as the Mayrian furrow (Fig. 7, sM). Each side 

 of the mesonotum is marked off for some distance from the median 

 portion of the segment by a distinct suture, which may be called the 

 parapsidal suture. The area thus cut off on each side is the parapsis. 

 The sides and the ventral portions of the metathoracic segment are 

 similar to those of the mesothorax, but smaller. It is possible to dis- 

 tinguish a metasternum, to which the coxa of the hind-leg is articulated, 

 a metepisternum and a metepimeron. Dorsally, however, the metano- 



FIG. 6. Thorax of a male Ponerine 

 ant, Streblognathus (cthiopicus in profile. 

 (Emery.) a' and a", Anterior and pos- 

 terior wings ; em and em' , meso- and 

 metathoracic epimera ; es and cs', epis- 

 ternites of the same segments ; cpn, epi- 

 notum ; g, metasternal gland; mtn. meta- 

 notum ; pet. petiole ; ppet, postpetiole ; 

 pn, pronotum ; ppt. parapteron ; sc, scu- 

 tum of mesonotum ; set, scutellum ; sf 

 and st', meso- and metathoracic ster- 

 nites ; stg', stg 2 . stg 3 and stg 4 , stigmata of 

 meso- and metathorax, epinotum and 

 petiole. The parts of the prothorax are 

 shaded with broken lines, those of the 

 mesothorax, epinotum and petiole are 

 unshaded, those of the metathorax are 

 shaded with unbroken lines ; the wing 

 articulations are dotted. 



