During fetal life, the primitive gut can be divided into three segments: foregut, midgut, and hindgut. Although these terms are often used in regard to segments of the primitive eviscerate, they are nevertheless used regularly to describe components of the definitive gut as well. gastrointestinal reaped ground segment of the primitive gut gives rise to specific embowel and gut-related structures in the of mature age. Components derived from the narrow pass proper, including the stomach and colon, open as swellings or dilatations of the primitive gut. In contrast, gut-related derivatives-that is, those structures that derive from the primitive gut but are not part of the gut proper-in general develop as outpouchings of the primitive gut. The blood vessels supplying these structures remain constant throughout development. Specialization of organs Four organs are subject to specialization in the kingdom Animalia. The first organ is the talk which is only present in the phylum Chordata.