modifications, due to individual taste or special knowledge of small groups, later writers had followed Linnæus and Cuvier. It was with a view of the animal kingdom not much clearer than this that Huxley began his work on the Medusæ of the tropic seas. He began to study them no doubt simply because they were among the most abundant of the animals that could be obtained from the ship. He made endless dissections and drawings, and, above all, studied their minute anatomy with the microscope. They were all placed among Cuvier's _Radiata_, but, as Huxley said in the first line of his memoir: "Perhaps no class of animals has been investigated with so little satisfactory and comprehensive result, and this not for the want of patience and ability on the part of the observers, but rather because they have contented themselves with stating matters of detail concerning particular genera and species, instead of giving broad and general views of the whole class, considered as organised upon a given type, and inquiring into its relations with other families." He found that fully developed Medusæ consisted each of a disc with tentacles and vesicular bodies at the margins, a stomach, and canals proceeding from it, and generative organs. He traced this simple common structure through the complications and modifications in which it appeared in the different groups of Medusæ, in all this work bringing out the prevailing features of the anatomy in contrast to the individual peculiarities. He shewed that microscopically all the complicated systems of canals and organs were composed of two "foundation-membranes," two thin webs of cells, one of which formed the outermost layer of the body, while the inner formed the lining of the stomach and canals in the thinner parts of the body, such as the edges of the umbrella-like disc, and towards the ends of the tentacles. These thin webs formed practically all the body. In the thicker parts there was interposed between them an almost structureless layer of jelly, placed like padding between the lining and the cloth of a coat. He shewed that blood-vessels and blood were absent, in which he has been confirmed by all other observers. He declared more doubtfully against the existence of a special nervous system, and it was not until long after, when the methods of microscopic investigation were much more perfect, that the delicate nerve-cells and nerve-fibres, which we now know to exist, were discovered.