THE CROP 



303 



boscis opens into a pharynx enclosed in a muscular sac (Figs. 303, 

 304, and 310). 



The pharyngeal sac, says Burgess, serves as a pumping organ to 

 suck the liquid food through the proboscis and to force it backwards 

 into the digestive canal. 



Meinert (" Trophi Dipterorum ") has made elaborate dissections of 

 the mouth and its armature, including the pharynx of several types 

 of Diptera, with its musculature. He describes the pharynx as the 

 principal, and in most Diptera, as the only part of the pump (antlia), 

 and says : " By the muscles of the pump (musculis antlice) the supe- 

 rior lamina of the pharynx is varied that the space between the two 

 laminae may be increased, 

 and the liquid is thus led 

 through the siphon formed 

 by the mouth-parts into the 

 mouth" (Fig. 81). 



The oesophagus. This is a 

 simple tube, largest in those 

 insects feeding on solid, 

 usually vegetable, food, and 

 smallest in those living on 

 liquid food. It usually 

 curves upwards and back- 

 wards, passing directly under 

 the brain, and merges into 

 the crop or proventriculus 

 either at the back part of the 

 head or in the thorax, its 

 length being very variable. 

 Its inner walls longitudin- 

 ally are folded and lined 

 with chitiu. 



gess. 



According to Newport, in 



the oesophagus of the Gryllidae, of the two layers of the mucous 

 lining the second is distinctly glandular and secretory, and in it 

 there are many thousands of very minute granular glandular bodies, 

 which probably secrete the "molasses" or repellent fluid often 

 ejected by these and other insects when captured. 



The crop or ingluvies. This, when present, is an enlargement of 

 the end of the oesophagus, and lined internally with a muscular coat. 

 It is very large in locusts (Fig. 298), Anabrus (Fig. 299), and other 

 Orthoptera (the Phasmidae excepted), in the Dermaptera, and most 



FIG. 304. Longitudinal section through the head 

 of Danais, showing the interior of the left half: mx, 



oe, oesophagus; ep, epipliaryiiij-cal valve; *, salivary 

 duct ; d. in, f. m, and el, as in Fig. 302. After Bur- 



