The little hat-like form, _Hydatina senta_, already referred to, is remarkable for the rapidity of its increase. The eggs are laid or deposited within a few hours of the time they are first seen within the transparent parent, and twelve hours later the young break from the shell and appear; so that in a comparatively few days the descendants of a single animal might possibly far exceed the population of the United States. The larger worms are with hardly any exception ornamented in some remarkable way, and in many the splendors of their decorations must be seen to be appreciated. The radiating coronets of _Serpulæ_[30] are of the most delicate and beautiful description, abounding in bands and markings of striking hues. _Pectinaria_ has upon its head a pair of combs that might be burnished gold; while _Eunicedæ_ and _Nereidæ_[31] have equally resplendent decorations. These charms of color, and they are of great variety, are seen by day; but at night many of these creatures assume the gift of phosphorescence, adding to the long list of marine light-givers that have been previously referred to. In four other families[32] are found the most beautiful light-givers of the group. Assuming that we have a certain species of the first mentioned in the aquarium, we may prepare for an extraordinary display. It is now snugly coiled up under a stone, perhaps fast asleep, and giving no evidence of its wondrous gift. Now touch it with the narrow handle of the dip-net, and a seeming electric spark is given out. But there is no electricity here: the light is a phosphorescent protest, and rapidly passes from scale to scale, until the whole animal stands out like a vivid shield of light against the bottom, glowing with the mysterious flame. If the worm is greatly disturbed, we are presented with a unique method of protection. Upon feeling the blow or attack, the light becomes intense, and flashes quickly from segment to segment, and along all the series of _elytra_; and, as the animal darts away, one or more of the scales become disconnected and are left behind, a luminous spot, to attract the attention of a possible follower, while the worm itself escapes. Nearly all the phosphorescent worms are rapid swimmers, and noted for their agile movements; and, as their scales are very readily disconnected, we may imagine in some cases a worm darting off and leaving a shower of sparks behind. In these worms the light is usually green.