THE INTERNAL STRUCTURE OF ANTS. 



33 



The thin chitinous lining of the oesophagus is covered with delicate 

 hairs which point backwards. At the base of the gaster the oesophagus 

 begins to dilate to form the ingluvies, or crop (Fig. 15, cr), a thin-walled, 

 pyriform bag, whose walls, like those of the oesophagus, consist of a layer 

 of longitudinal and one of transverse or ring-shaped muscle fibers and 

 a delicate chitinous lining. In the oesophagus the chitinous lining is 

 beset with fine hairs pointing backwards. There are no glands in the 

 crop and the chitinous walls completely resist the absorption of food, 

 so that this organ serves merely as a reservoir for the liquid that has 

 been imbibed or lapped up directly or sucked out of the more solid 



FIG. 15. Gaster of female Myrmica ntbra in sagittal section. (Janet.) ppt, Post- 

 petiole : sir, stridulatory organ; gs'-gs a , first to sixth gastric segments: lit, heart; 

 f. cardiac valve ; pc, pericardia! cells ; u, urate cell ; /, adipocyte ; on, cenocyte ; ot, 

 ovarian tubules : od, oviduct ; nt, uterus ; rs, receptaculum seminis : be, bursa copu- 

 latrix ; rg. vagina ; rr, vulva ; st, stylets of sting ; gt, gorgeret ; pg, poison gland ; 

 ag, accessory gland. Remaining letters as in Fig. 13. 



substances moulded in the infrabuccal chamber. Forel aptly calls the 

 crop " the social stomach," because the food it contains is at least in 

 great part fed by regurgitation to the other ants of the colony or to 

 the brood. The crop is remarkably distensible, especially in certain 

 Camponotinae, like the honey-ants, so that its replete or deplete condition 

 determines the volume, and in a measure also the shape of the gaster 

 in the worker. 



The crop is succeeded by a remarkable structure, the proventriculus. 

 or pumping stomach, which has been carefully studied by Forel ( 1878^ ) 



