- the middle part of the alimentary canal in vertebrate embryos
- the endoderm-lined portion of the digestive tract of arthropods
- The middle section of the digestive tract in a vertebrate embryo from which the ileum, jejunum, and portions of the duodenum and colon develop. Also called mesenteron.
- The middle portion of the digestive tract of certain invertebrates, such as arthropods, lined with an enzyme-secreting tissue and serving as the main site of digestion and absorption.