Those cousins of the Shark,--the Skate and the Dog-fish,--are more careful of their eggs. Have you ever found their empty eggs on the sea shore? Children call them "mermaids' purses." But they are more like little horny pillow-cases than purses. When first laid, the Dog-fish's egg has a very long string or _tendril_ at each corner. As the fish lays the egg, she winds these tendrils round and round a sea-plant; thus the egg is fixed firmly until the young one is ready to escape from within (_see_ p. 49). The Skate's egg is much the same, only there is no tendril, but a curved hook at each corner. These hooks, of course, serve as anchors to hold the egg: no doubt they catch in weeds and stones. One fish, you see, ties her eggs with strings, the other uses anchors. These large "purse eggs" are like cradles, and the baby Skates do not slip out of them until they are quite ready to look after themselves in the ocean. There are fish in the sea which take great pains to save their eggs and babies from harm; they will even defend them at the risk of their own lives. Of course these careful parents do not have huge families, like the Cod. No; the fish that care for their young have small families, but the babies have a much better chance of living than the baby Cod. It is one of Nature's wise laws. Our common Stickleback--"Tiddler," or "Red-throat," as boys call him--builds a nest in ponds. He has a seaside cousin, the fifteen-spined Stickleback, who is also a nest-builder. This little fish is fairly common round our coasts, living in weedy pools by the shore, where it devours any small creature unlucky enough to come near. It is about six inches long, this sea Stickleback, with a long snout, and its body is very thin near the tail. To build his nest, this little fish chooses a quiet corner, then gathers pieces of green and purple seaweed. He takes the pieces in his mouth, pushing them about until the shape is to his liking. Having got his nursery to the right size and shape, the little builder next fastens it together. How can he do this? What mortar can he find in the sea? It is quite simple. He uses threads, which come from his own body. He swims round the nest, again and again; and, each time, a thread is spun, binding the clump of weed into a safe, tight nest for the eggs. When the task is done there is a weed-nursery about the size of your fist. Now all is ready for the eggs to be laid by the female Stickleback. You would expect them to be kept in a hole amid the nest, would you not? Instead of that, they are tucked a few here, a few there, in the weed.