Similar devices for protecting the young in their earliest helpless stages of growth from the egg-shell are found in all classes of animals. What is very curious is the fact that, of two closely allied animals, one species will recklessly lay its eggs and leave them, whilst another has special arrangements for retaining in the parent’s body the eggs as they develop, and so preserving them from danger. Such parents are called “viviparous.” Of course, in all viviparous animals, as well as in those which lay their eggs in hard shells, the fertilisation of the egg must be effected within the maternal body. Amongst our common fishes there is the viviparous blenny, often found in pools at low tide on the seashore. All the other British fresh-water and marine fishes lay their eggs and abandon them, excepting some sharks, dog-fish, and skates, which are viviparous; others of the shark and skate tribe lay eggs of large size encased in hard, horny shells. Every one knows that frogs and toads lay their eggs, but there are some kinds in which the eggs remain inside the mother’s body during the development of the young, which only escape into the world as well-formed little frogs. All the hairy, warm-blooded quadrupeds known as “the mammals” are viviparous, except the duck-mole and the spiny ant-eater of Australia. These extraordinary little “beasts” lay eggs like those of a bird. The most ingenious devices for the protection of the young are (as perhaps those who believe in the superior intelligence of the male would expect) put into practice by the male parent. Thus, there is a large fish in tropical rivers which takes the eggs laid by the female into his capacious mouth, and swims about with them for three or four weeks, giving them the advantage of a current of water which runs through his mouth to his gills. When the young hatch they swim out of their fond father’s mouth. The male of pipe-fishes and of the little “sea-horse” receives the eggs laid by the female into a pouch excavated along his ventral surface. There the young hatch, and are guarded by the nursing father. On the other hand, some fathers impartially eat their own young, as well as those of other parents, and the mother has a hard job to protect her offspring. A female octopus (the poulp or eight-armed cuttle-fish) sits over her eggs in a nest built of pebbles at the bottom of the sea (or of an aquarium tank in the instance studied by me many years ago at Naples), and squirts a stream of pure sea-water over them. She resents the approach of a fish or a crab or a landing-net with splendid fury and recklessness of attack. Often the males of fishes, frogs, and birds guard the eggs, or guard the nest where the female is occupied in caring for the eggs or the young.