"Annales"; the histories of Roman Literature by M.
- Tacitus, Histories, iii.
At present, therefore, classifications of the Hydromedusae have a more or less tentative character, and are liable to revision with increased knowledge of the life-histories of these organisms. Many groups bear at present two names, the one representing the group as defined by polyp-characters, the other as defined by medusa-characters.
Zahn (1900) and Julicher (1906); the histories of the apostolic age by C. von Weizsdcker (1892), A.