Describe the digestive system of cockroach with the help of neat, labeled diagram.

The digestive system of cockroach consists of an alimentary canal and the associated digestive glands. 

Pre oral cavity is surrounded by the mouth parts. It is divided into 2 chambers.

• Cibarium 
• Salivarium

The alimentary canal of cockroach is a long tube and is coiled. It has 3 regions.

• Foregut 

It is also known as stomodaeum. It is internally lined by a chitinous cuticle. Mouth opens into the pharynx, it leads into oesophagus, it opens into a sac called crop. Gizzard is a thick-walled muscular part with 6 chitinous teeth. It acts as a grinding mill and also as a sieve. There is a membranous projection of the gizzard into the mesenteron in the form of a funnel called stomodeal valve.

• Midgut

It is also called mesenteron or ventriculus.  6 to 8 finger like hepatic caecae arise from the midgut. Anterior part is secretory with many gland cells. It secretes many enzymes and peritrophic membrane. Posterior part is absorptive.

• Hindgut

It is also known as proctodaeum. It has 3 regions.

Ileum: It is a short tube behind the midgut. Malphigian tubules open into it.

Colon: It is a long-coiled tube. It opens into rectum.

Rectum: It is a short, wide part which opens out the through the anus. It has 6 folds called rectal papilla.

Digestive glands: 

• Salivary glands: A pair of salivary glands attached to the ventrolateral sides of the crop. Each salivary gland has two lobes and two saclike salivary receptacles. Saliva contains amylase enzyme.
• Hepatic caecae: 3 glandular cells of the mesenteron secrete enzymes such as maltase,
  invertase, protease and lipase.