THE present work is the continuation of a series of studies (Al-Hussaini,1945-7) attempting to correlate the structure of the alimentary canalwith the feeding habits of teleosts. These earlier studies were based on distantlyrelated species and thus the differences observed and described mightwell be due to congenital factors rather than to purely adaptive causes—of thisno certain answer can yet be given. The present study is an attempt to excludecongenital factors as nearly as possible by choosing three closely allied species