From the filaments here described, others more slender still depend at regular intervals, which curl up like vine tendrils upon the principal stem. The whole can be spontaneously elongated or slowly withdrawn within the body of the Beroë, where they lie enclosed in two sheaths until again required for use. These interior 'sheaths,' which resemble in shape the drone of a bag-pipe, are easily seen, being almost the only parts which are not perfectly transparent. They are whitish in colour, and semiopaque. (Plate 6 contains a sketch of the Beroë, drawn from nature.) I may mention that the paddles, with their comb-like array of cilia, flap successively in regular order from the top to the bottom of each row. This wave-like movement takes place simultaneously in all the rows, when the animal is in full vigour. The organs of progression in the _Pulmonigrade_ Acalephæ, as their name imports, bear certain resemblance to the lungs in respiration. They move by the expansion and contraction of their umbrella-shaped bodies. Graceful and elegant indeed are the motions of these creatures. I have seen small specimens about the size of a sixpence, advance, in three springs, from the bottom to the top of a large vase in which they were confined. In descending they turn over and allow themselves to sink gradually as if by their own weight. The third division of the Acalephæ is termed _Physograde_. The most common member of this group is the _Physalus_, so well known to all sailors under the name of the Portuguese Man-of-War. It is buoyed up by air bladders--in fact, its entire body appears as one bladder, which the animal is enabled to contract or expand at will. At first glance the _Physalus_ appears to belong to quite a different family--suffering under some maltreatment; for from its lower side, what seem a number of entrails, of all shapes and sizes, hang down. When the upper surface or crest of its swimming bladder projects above the waves, it has a beautiful appearance, spangled with rays of purple, blue, and gold. This formation acts as a kind of sail, by means of which the creature is enabled to glide along with considerable speed. This Physalus is a somewhat mysterious being, and zoologists have not as yet been able to determine many points connected with its structure and development. The _Cirrigrade_ Acalephæ, too, are a singular family. They exhibit a higher stage of development than those already alluded to, and possess a kind of skeleton embedded within their gelatinous bodies. The _Porpita_ and _Velella_ are examples of this class, but for detailed descriptions I must refer the reader to larger works which treat on the subject.