Once the undigested and unabsorbed substances enter the caecum, their backflow is prevented by-

Step-by-step solution

The Ileum opens into the large intestine, which has caecum, colon and rectum. The caecum is a small blind sac which hosts some symbiotic micro-organisms. The entry of ileum and caecum is guarded by ileo-caecal valve. The undigested, unabsorbed substances called faeces enters into the caecum through this ileo-caecal valve. This valve prevents the back flow of the faecal matter. It is temporarily stored in the rectum till defaecation.