Haeckel had come chiefly to study the medusæ. But this led him on much further to a great zoological problem. In his _General Morphology_ he had expounded his brilliant ideas on the subject of individuality, and now he encountered in the flesh one of the greatest marvels of animal individuality. He had shown how the higher individual is always made up of a community, a kind of state, of lower individuals. In the simplest instance there are the cells. Each of them is an individual. Millions of these individuals, banded together with division of labour for great collective operations, make up the human frame, and therefore the human “individual.” In the same way others form a beetle, a snail, or a single medusa. Sometimes, however, these higher individuals enter in turn into social combinations to form still higher communities. Human beings form social commonwealths, with division of labour among the individuals. Bees and ants form their communities in the same way. But in the latter cases the texture of the community seems to be much looser than in the preceding one. It is not so easy for the imagination to grasp a human commonwealth or a colony of bees as a real “over-individual.” It is, therefore, extremely instructive to find that at least one animal community of this kind is of so firm a texture that even on the most superficial examination it is recognised at once as an individual. This is found in one of the groups of the medusæ, the siphonophores, or social medusæ. A number of single medusæ, each of which corresponds to what we regard as the individual man, combine and form a new body, a social individual. As citizens of this new state they have introduced the most rigid division of labour. One medusa does nothing but eat, and it thus provides nourishment for the rest, as they are all joined in one body. Another accomplishes the swimming movement; another has been converted entirely into a reproductive organ. In a word, the whole has become a “unity” once more, equipped with its various organs like any large body. Sometimes thousands of separate medusæ enter into the structure of one of these wonders of the deep. And as each of the medusæ is generally a very pretty, flower-like creature, the social groups with their charming colours look like floating garlands of flowers made of transparent and tinted crystal. Their beauty would soon fix Haeckel’s attention, but their bearing on his theory of individuality would give them an even greater value. For several years he had searched most attentively in the animal world for these “over-individuals” of the highest class. In the morphology he had had to be content with an old illustration of something of the kind, the star-fish. It was supposed to be a combination of vermalians. In this case the hypothesis has broken down, though there was a good deal to be said for it at first, and it was abandoned by him afterwards. But now, when he saw enormous numbers of