Explain the digestive system of cockroach with the help of a labelled sketch.

The alimentary canal present in cockroach is divided into three regions that foregut, midgut and hindgut.
(i) Foregut includes mouth cavity, pharynx, oesophagus, crop and gizzard.
(ii) Mouth cavity is a small space, surrounded by mouth parts. Food is crushed and acted upon by the salivary secretion in mouth.
(iii) The mouth opens into a short tubular pharynx, leading towards the narrow tubular passage called oesophagus into a sac-like structure called crop which acts as a storage organ. 

(iv) The crop is further followed by gizzard (proventriculus). Gizzard the structure composed of thick circular muscles and thick inner cuticle forming six highly chitinous plates called as teeth. It associated with the grinding and crushing of food particles. Entire forgut is lined by a thick cuticle.
(v) Midgut or mesentron is about one-third middle part of alimentary canal. The internal lining of midgut is an endodermal epithelium of columnal cells raised into several small villi like folds.
(vi) Anterior most part of midgut surrounding the stomadaeal valve is called cardia and finger like blind processess are called as enteric or hepatic caeca, present the junction of foregut and midgut.
(vii) A ring of yellow filamentous structures formed between the midgut and hindgut are called Malpighian tubules help in the removal of excretory products from haemolymph.
(viii) Hindgut is the remaining one-third posterior part of alimentary canal. It is relatively thicker than the midgut is lined by cuticle and ectodermal epithelium. 
(ix) Hindgut is differentiated into three parts, i.e., anterior ileum, middle colon and posterior rectum. Ileum is short and relatively narrower and its cuticle bears minute spines. Colon is the longest, relatively thicker and a coiled part of hindgut. Rectum is a small and oval chamber that opens out through anus.