Explain the three parts of alimentary canal.

1. Digestive system of cockroach consists of mouthparts, alimentary canal and salivary glands.

2. Mouthparts: Pre-oral cavity present in front of the mouth receives food. It is bounded by chewing and biting type of mouth parts. 

3. These are movable, segmented appendages that help in ingestion of food. 

The mouthparts of cockroach comprises of:

 a. Labrum: It forms the upper lip. It is a single flap-like movable part which covers the mouth from upper side. It forms an anterior wall of pre¬oral cavity. 

Function: It is useful in holding the food during feeding. 

b. Mandibles: These are two dark, hard, chitinous structures with serrated median margins.They are true jaws present on either side, behind the labrum. Function: They perform co-ordinated sidewise movements with the help of adductor and abductor muscles to cut and crush the food. 

c. Maxillae: These are the accesssory jaws. They are also called as first pair of maxillae. These are situated on the either side of mouth behind the mandibles. Each maxilla consists of sclerites like cardo, stipes, galea, lacinia and maxillary palps. 

Functions: Maxillae hold food, help mandibles for mastication. They are also used for cleaning the antennae and front legs. Maxillary palps act as tactile organs. 

d. Labium: It forms the lower lip. Labium is also known as second maxilla which covers the pre-oral cavity from the ventral side. It is firmly attached to the posterior part of head. It has three jointed labial palps which are sensory in function. 

Function: It is useful in pushing the chewed food in the pre-oral cavity. It prevents the loss of food falling from the mandibles, while chewing.

e. Hypopharynx: Hypopharynx is also known as lingua. It is a somewhat cylindrical single structure, located in front of the labium and between first maxillae. The salivary duct opens at the base of hypopharynx. Hypopharynx bears comb-like plates called super-lingua on either side. Hypopharynx is present at the centre of the mouth.

Function: It is useful in the process of feeding and mixing saliva with food,

4. Alimentary canal: It is long a (6 – 7cm) tube of different diameters with two openings.