It would not be possible to find a more perfect example of regional colouration. Not only is each organ differently coloured, but the important parts of each organ, like the ridge of the crest, the bases of the tentacles, and the thread-cell bearing ridges of the tentacles, are also emphasized with deep colour. _Velella._ This beautiful creature, which sometimes finds its way to our shores, is like a crystal raft fringed with tentacles, and having an upright oblique crest, or sail. The margins of the disk and crest are often of a beautiful blue colour, and the canals of the disk become deep blue as they approach the crest. The polypites may be blue, purple, green, or brown. _C. Medusidæ._ The structure and colouration of the true Medusæ are so like that of the medusiform larvæ of the other Hydrozoa, that they need not be particularly described. _D. Lucernarida._ Of this sub-class we need only cite the _Lucernaria_ themselves; which are pretty bell-shaped animals, having the power of attaching themselves to seaweeds, etc., and also of swimming freely about. Round the margin are eight tufts of tentacles, opposite eight lobes, the membrane between the lobes being festooned. In _L. auricula_, a British species, the membrane is colourless and transparent, the lobes bright red, or green, and the tentacles blue. As a group the Hydrozoa display regional colouration in a very perfect manner. II. ACTINOZOA. It is not necessary to trace the colouration through all the members of this group, but we will trace the variation of colour through two species of anemonies, which have been admirably studied by Dr. A. Andres.[27] The first column shows the general hue, the second the tints of that hue which are sufficiently marked to form varieties as cochineal red, chocolate, bright red, rufous, liver-coloured, brown, olive, green and glaucous. The third column gives the spotted varieties, from which it will be seen that the chocolate, liver, and green coloured forms have each coloured varieties. It will be seen that the range of colour is very great, passing from pale pink, through yellowish-brown to blue-green. -----------+-----------+-----------+---------------- Prevailing | Uniform | Spotted | colour. |varieties. |varieties. | Allied species. -----------+-----------+-----------+---------------- White. | ? | | A. candida. " | coccinea. | | " | chiocca. | tigrina. | Red. | rubra. | | " | rufosa. | | Yellow. | hepatica. | fragacea. | " | umbra. | | " | olivacea. | | " | viridis. | opora. | " | glaucus. | | Blue. | ? | | -----------+-----------+-----------+---------------- Varieties of Actinea Cari. The following brief descriptions illustrate the distribution of the colour:-- _Actinea Cari._