12 BRITISH ANTS. 



producing organ is situated at the extreme base of the first gastric 

 segment. This organ consists of a file, formed by very fine trans- 

 verse ridges, situated at the base of the segment, in the centre of 

 its dorsal area. The edge of the preceding segment is sharp, turning 



Epinotum Scale Gaster 



Sting 



Pedicel 1st 2nd 3rd 4th 5th 

 Gastric segments 



Fig. 21. Abdomen of Ponera coarctata Q 



slightly downward, or inward, and is thus able to scrape the file, 

 when the two segments move on each other. These structures are 

 present in the Ponerinae and Myrmicinae, but appear to be absent 

 in the Camponotinae and Dolichoderinae. The sculpture, however, 



Epinotum Spine Petiole Post-petiole 



Gaster 



Pygidium 



Pedicel 1st 2nd 3rd 4th 

 Gastric segments 



Fig. 22. Abdomen of Myrmica ruginodis ^. 



of the corresponding surfaces in the genus Donisthorpea, etc., is 

 modified, and though there is no true stridulating organ, it is 

 probable that some sounds may be produced when these surfaces 

 are rubbed together. 



5th Dorsal gastric segments 

 5th Ventral gastric segments 



Fig. 23. Abdomen of Tapinoma erraticum ^ . 



The apical segment of the gaster is called the pygidium, its dorsal 

 plate being the epipygium, and the ventral one the hypopygium ; the 

 former is nearly always visible from above, except in some genera 

 where it is entirely hidden beneath the preceding segment. The 



