The _Anthomedusa_ in form is generally deep, bell-shaped. The sense organs are typically ocelli, never otocysts. The gonads are borne on the manubrium, either forming a continuous ring (Codonid type), or four masses or pairs of masses (Oceanid type). The tentacles may be scattered singly round the margin of the umbrella ("monerenematous") or arranged in tufts ("lophonematous"); in form they may be simple or branched (Cladonemid type); in structure they may be hollow ("coelomerinthous"); or solid ("pycnomerinthous"). When sessile gonophores are produced, they may show all stages of degeneration. _Classification._--Until quite recently the hydroids (Gymnoblastea) and the medusae (Anthomedusae) have been classified separately, since the connexion between them was insufficiently known. Delage and Hérouard (HYDROZOA [2]) were the first to make an heroic attempt to unite the two classifications into one, to which Hickson (HYDROZOA [4]) has made some additions and slight modifications. The classification given here is for the most part that of Delage and Hérouard. It is certain, however, that no such classification can be considered final at present, but must undergo continual revision in the future. With this reservation we may recognize fifteen well-characterized families and others of more doubtful nature. Certain discrepancies must also be noted. 1. _Margelidae_ (= medusa-family _Margelidae_ + hydroid families _Bougainvillidae_, _Dicorynidae_, _Bimeridae_ and _Eudendridae_). Trophosome arborescent, with hydranths of _Bougainvillea_-type; gonosome free medusae or gonophores, the medusae with solid tentacles in tufts (lophonematous). Common genera are the hydroid _Bougainvillea_ (figs. 12, 13), and the medusae _Hippocrene_ (budded from _Bougainvillea_), _Margelis_, _Rathkea_ (fig. 24), and _Margellium_. Other hydroids are _Garveia_, _Bimeria_, _Eudendrium_ and _Heterocordyle_, with gonophores, and _Dicoryne_ with peculiar sporosacs. [Illustration: After Haeckel, _System der Medusen_, by permission of Gustav Fischer. FIG. 52.--_Tiara pileata_, L. Agassiz.] 2. _Podocorynidae_ (= medusa-families _Thamnostomidae_ and _Cytaeidae_ + hydroid families _Podocorynidae_ and _Hydractiniidae_). Trophosome encrusting with hydranths of _Bougainvillea_-type, polyps differentiated into blastostyles, gastrozoids and dactylozoids; gonosome free medusae or gonophores. The typical genus is the well-known hydroid _Podocoryne_, budding the medusa known as _Dysmorphosa_; _Thamnostylus_, _Cytaeis_, &c., are other medusae with unknown hydroids. _Hydractinia_ (figs. 9, 10) is a familiar hydroid genus, bearing gonophores. 3. _Cladonemidae_.--Trophosome, polyps with two whorls of tentacles, the lower filiform, the upper capitate; gonosome, free medusae, with tentacles solid and branched. The type-genus _Cladonema_ (fig. 20) is a common British form.