and gives off pure oxygen. Submarine ships are now being provided with a dress or outfit of this description for each member of the crew, so that in the case of the entrance of water into the submarine, every man can put on his “oxygen helmet,” and one by one, when the ship is full of water, they can pass out by the conning tower and float to the surface. The perfected diving dress, with self-contained diluted oxygen supply and other improvements, has been constructed by Siebe, Gorman, and Co., and was exhibited by Dr. Leonard Hill at a soiree of the Royal Society. XXVIII SPARROWS, TROUT, AND SELECTIVE BREEDING The talk about the urgent need for the destruction of sparrows reminds me that the word “sparrow” is applied commonly in this country to at least two very different but common birds. No doubt farmers and gardeners know well enough the house-sparrow (_Passer domesticus_ or _Fringilla domestica_ of Linnæus), which is the one they consider injurious. But some boys and some newly-fledged proprietors of country places may inadvertently confuse the house-sparrow with a very different bird, though only a little smaller and of a general brown colouring, also called “sparrow,” namely, the hedge-sparrow (_Accentor modularis_). The hedge-sparrow is a true denizen of the country. It does not live on grain, but on insects and grubs, and is useful on that account to agriculturists. Its eggs are pure blue. A spotted egg of a cuckoo laid amongst them readily catches the eye, so that cuckoos’ eggs are often found in hedge-sparrows’ nests. It seems that it is all a mistake on the part of the cuckoo hen when this occurs. The strain of cuckoos properly attached to hedge-sparrows lay a beautiful blue egg differing only in its somewhat larger size from those of the hedge-sparrow itself, and hence difficult to detect. These blue cuckoo-eggs—proper to cuckoos which make use of the hedge-sparrow as foster-mother—escape detection both by boys and the foster-parents, and successfully hatch out and propagate the race of blue-egged cuckoos with a memory and a sense of smell which bring them back if they are hen-birds to the little hedge-sparrow’s nest when they are grown up and have an egg to dispose of. The spotted grey or brownish eggs are, if not discovered by boys, ejected (there is reason to believe) by the hedge-sparrows themselves. They were deposited by mistake by some pippet-loving or warbler-seeking strain of cuckoo in a hurry, or are throw-backs to a common ancestral colouring of the egg due, perhaps, to the male parent not being of the true blue strain. A very fine series of “clutches” and nests of hedge-sparrow, robin, shrike, reed-warbler, pippet, yellow-hammer, and other birds with the accompanying cuckoo’s egg may be seen in the Natural History Museum, and they show how closely the parasitic egg often resembles that of the foster-parent, though striking failures also occur.