In Figs. 70-73 we have the Acalephian and Hydroid stages of the Clytia (Fig. 73), another very pretty little Jelly-fish, closely allied to the Oceania. When first hatched, like the Oceania, it is very convex, almost thimble-shaped (see Fig. 70), but a little later the disk flattens and becomes more open, as in Fig. 71. In Fig. 72, we have a branch of the Hydroid, a Campanularia, greatly magnified, with the annulated reproductive calycle attached to it, and crowded with Jelly-fishes ready to make their escape as soon as the calycle bursts. The adult Clytia (Fig. 73) is somewhat smaller and more active than the Oceania, and is easily recognized by the black base of its tentacles, at their point of juncture with the margin of the disk. It is more commonly found at night, than in the day-time, being nocturnal in its habits. [Illustration: Fig. 70. Young Clytia just escaped from the reproductive calycle.] [Illustration: Fig. 71. Clytia somewhat older than Fig. 70.] [Illustration: Fig. 72. Magnified portion of Hydrarium of Clytia.] [Illustration: Fig. 73. Adult Clytia; twice natural size.] _Zygodactyla_. (_Zygodactyla groenlandica_ AG.) Little has been known, and still less published, of this remarkable genus of Jelly-fish (Figs. 74, 75) up to the present time. The name Zygodactyla, or Twinfinger, was given to it by Brandt, from drawings made by Mertens, who had some opportunity of studying it in his journey around the world. These drawings were published in the Transactions of the St. Petersburg Academy. In the year 1848 Professor Agassiz read a paper upon one of the species of this genus belonging to our coast, before the American Academy, in which he called it Rhacostoma, not being aware that it had already received a name, and gave some account of its extraordinary phosphorescent properties. The name Rhacostoma must of course yield to that of Zygodactyla, which has a prior claim. [Illustration: Fig. 74. Zygodactyla seen from above.]