56 ON THE ANATOMY OF THE FLY. 



without exserting the proboscis, and gradually reimbibe it. As 

 such a drop entirely surrounds the palpi, I think it not unlikely 

 they are the organs of sensation concerned in this act, and per- 

 haps the seat of the special sense of taste. In the larva the food 

 passes directly from the pharyngeal pouch into the proventri- 

 culus. 



The chyle stomach extends the whole length of the thorax ; 

 it is divided by reticulations of circular and longitudinal bands 

 of muscular fibres, between which the membranous coat bulges, 

 so that its inner surface is covered with little square pits. It is 

 lined with conical cylinder epithelium. It is much longer in the 

 larva than in the perfect insect, and four ca)cal glands, about half 

 its length, open into its anterior extremity. These disappear in 

 the pupa,<and are not redeveloped in the imago. 



The small intestine extends from the stomach to the opening 

 of the bile tubes, about three quarters of an inch ; its upper 

 end is like the chyle stomach, which passes insensibly into it, 

 but it soon looses its reticulated structure, and its muscular coat 

 becomes uniform and thin. Both circular and longitudinal 

 muscular fibres may be traced in it.* In the larva the bile tubes 

 open at the posterior extremity of the stomach, and the small 

 intestine first appears in the pupa. 



The bile tubes ( Plate IV, Figs. 1 and 7 ) commence in blind 

 extremities, and unite in pairs, until they open into the in- 

 testine, by two large ducts. They are very numerous, and occupy 

 the dorsal portion of the abdomen ; they have a beaded outline 

 and contain irregular nucleated cells, yellow pigment, and fat 

 granules. I have found occasionaly dumb bell crystals in the 

 bile tubes, but have failed to detect uric acid in them, either in 

 the larva or imago. 



* Its peristaltic action is very vigorous and may be observed plainly 

 in the smaller house fly, the sides of the abdomen of which are very 

 transparent. It may be seen also in the immature Blow-fly. 



