DISSECTION OF A COCKROACH 17 



walled muscular division, closely applied to the crop, i, 2, 

 and 3 belong to the fore-gut, which is developed as an 

 infolding of the integument of the embryo from the mouth. 

 It is lined throughout by chitinous cuticle. (4) The 

 stomach or mid-gut, a narrow cylindrical tube, marked 

 at its beginning by eight blind tubes which open into 

 it, and at its termination by a large number of fine threads, 

 the Malpighian tubules or excretory organs. The stomach 

 has no chitinous cuticle of its own. Beyond it comes the 

 intestine or hind-gut, an infolding of the integument of the 

 embryo from the anus. It is Hned, like the fore-gut, with 

 chitinous cuticle. The hind-gut is divided into the following 

 parts : — (5) The small intestine, very short and narrow. To 

 this the Malpighian tubules properly belong. (6) The colon, 

 wide in front, but narrowing ' gradually backwards. It is 

 thrown into a single coil. (7) The rectum, a dilated muscular 

 chamber ending at the anus. 



Clear and examine the salivary glands. These are two pairs 

 of white branching glands, lying on either side of the crop. 

 Between the glands of each pair lies a salivary receptacle. 

 The ducts from the glands unite, and open into the much 

 larger duct of the receptacles, which discharges into the 

 mouth. Cut out one salivary gland. Stain it with carmine, 

 mount in glycerine, and examine with the microscope. Observe 

 the nucleated epithelium and the chitinous lining of the 

 duct with its spiral thickening. Cut out the gizzard and 

 lay it open on one side. Then remove the soft parts with hot 

 caustic potash solution, and mount in balsam. Observe the 

 six stout teeth (thickenings of the chitinous lining) and their 

 varying shape, the folds between the teeth, the hairy patches, 

 one below each tooth, and the hairy ridges beyond. The 

 chitinous lining is continued beyond the gizzard into the 

 stomach, where it forms a free inner tube which is thrown into 

 many longitudinal folds. 



The food is first of all received into the crop, where it is 

 mixed with the salivary fluid, and undergoes maceration and 

 partial digestion. It is passed on to the gizzard, which acts as 

 a masticatory organ, and also as a strainer, detaining coarse 

 particles. When the food enters the stomach, absorption of 

 the dissolved matter takes place, and the nutritive fluids enter 

 the blood, which bathes the exterior of the alimentary canal. 



