We find in another species a still more perfect rigging. In it (_Rataria_) the crest is supplied with muscular bands, by means of which the sail can be lowered or raised at pleasure. These adaptations of structure are full of interest. Nothing can be more admirable than the sailing-gear of these little creatures. They have to traverse the surface of the ocean amidst all diversities of weather. Paddles alone would not suffice for them. They must be enabled to take advantage of the winds. Sails, therefore, are added, and the mightiest agents in nature are commissioned to speed the little voyagers on their way. We have already mentioned that some of the jelly-fishes possess the power of stinging. Only a few of the larger species, however, seem to be thus endowed; and the name sea-nettle is by no means applicable to the class as a whole. The poisonous fluid which produces the irritating effect on the skin, and no doubt paralyses the creatures upon which the jelly-fish feeds, is secreted by the arms. By means of its poison-bearing tentacles, the soft, gelatinous medusa is more than a match for the armed crustacean and the scale-clad fish. We take from Professor Forbes the following graphic description of one of the stinging species:--'The _Cyanaea capillata_ of our seas is a most formidable creature, and the terror of tender-skinned bathers. With its broad, tawny, festooned, and scalloped disk, often a full foot or more across, it flaps its way through the yielding waters, and drags after it a long train of ribbon-like arms, and seemingly interminable tails, marking its course when its body is far away from us. Once tangled in its trailing "hair," the unfortunate who has recklessly ventured across the graceful monster's path too soon writhes in prickly torture. Every struggle but binds the poisonous threads more firmly round his body, and then there is no escape; for when the winder of the fatal net finds his course impeded by the terrified human wrestling in its coils, he, seeking no contest with the mightier biped, casts loose his envenomed arms, and swims away. The amputated weapons severed from their parent body vent vengeance on the cause of their destruction, and sting as fiercely as if their original proprietor itself gave the word of attack.' We now approach the most extraordinary portion of the history of these creatures. Recent investigations have brought to light the most interesting facts respecting their reproduction and development. It is now known that the young jelly-fish passes through a series of transformations before reaching its perfect state.