The gut forms very early during embryological development (ontogeny) and shows some of the same stages of development as in the evolution of the vertebrate gut, some larval fish having portions of their gut which are ciliated, for example. The general character and even the length of the gut may change during development. The gut appears to shorten, for example, in fish in which the larval stage is herbivorous and the adult stage is carnivorous. In other fish the gut length remains relatively constant in proportion to body size throughout life