THE STRUCTURE OF INSECTS. 



11 



(pyloric end) the urinary tubes (vasa urinaria, Fig. 4, ur) 

 arise. These are arranged in ten groups of about fifteen 

 tubes, so that there are about one hundred and fifty long, 

 fine tubes in all. 



The intestine (ileum) lies in the fifth and sixth abdominal 

 segments. 



Behind the intestine is the colon, which is smaller than 

 the intestine proper, and makes a partial twist. The colon 

 suddenly expands into the rectum, with six large rectal 

 glands on the outside, held in place by six muscular bauds 

 attached anteriorly to the hinder end of the colon. The 

 rectum turns up toward its end, and the vent is situated 

 just below the supra-anal 

 plate. 



Having described the diges- 

 tive canal of the locust, with 

 which that of the beetle (Fig. 

 6) and the fly (Fig. 7) may 

 be compared, we may state in 

 a summary way the functions 

 of the different divisions of 

 the tract. The food after be- 

 ing cut up by the jaws is acted 

 upon while in the crop by the 

 salivary fluid, which is alka- 



linp id n<!<?p<ps! flip vrm. Fia 5 --Transverse section of the pro- 



ine, ail( , prop- ventriculus of Gryllus cinereus of 



pvtv -JB in vpi'fpVutntpa r>f Europe; muc, muscular walls; r, 



n J> as Jrates, OI hornf ridge between the large teeth. 



rapidly transforming the -After Minot. 

 starchy elements of the food into soluble and assimilable 

 glucose. The digestive action carried on in the crop (inglu- 

 vies) then, in a vegetable-feeding insect like the locust, 

 results in the conversion of the starchy matters into glucose 

 or sugar. This process goes on very slowly. When diges- 

 tion in the crop has ended, the food submitted to an ener- 

 getic pressure by the walls of the crop, which make peri- 

 staltic contractions, filters gradually through the short, small 

 proventriculus, directed by the furrows and chitinous 



