Perhaps the simplest plan to adopt is to cut open a mussel and throw it into the tank. A considerable deal of amusement, moreover, is often to be obtained by watching the fishes engaged at such a meal. How they toss the valves of the Mytilus about, and snap at each other's tails! How vexed they become if by accident the shelly dish is turned topsy-turvy, and resists all their manœuvres to reverse it so as to get at the meat! The valves of a large mussel will sometimes be literally cleaned out by some half dozen Blennies in the course of an hour. I have noticed a singular fact in connection with the Blenny--namely, _that they do not all increase in size as they grow older_. Out of five that I kept domesticated for more than two years, one specimen remained at the end of that period of the same size as when I first made its acquaintance in a rock-pool by the sea-shore, while its companions had greatly increased their proportions. But let me in justice add, that if my little finny pet failed to increase in corpulency, it gained largely in intelligence. Who is there that has not seen children, short in stature, and comparatively old in years, who deserve the epithet applied to them by the vulgar, of 'little--but _knowing_.' This remark would apply with great truth to my 'little Dombey' fish. Before becoming expert in carrying out the plan (which will be fully detailed hereafter) for clarifying the water of an aquarium which has become opaque from superabundant vegetative growth, I had to submit to many annoying failures. Thus it was in a certain instance. I had cleaned out my tank, refilled it with partially purified water, and again inserted the various animals constituting my 'stock.' Emboldened by the success which had attended my operations, I thought a still further dose of diluted acid might be added, in order thoroughly to remove the greenish hue of the water. A few minutes showed me the folly of not letting well alone, for soon flakes of discharged vegetation were precipitated to the base of the vessel, covering it with a coating of fur. The poor Blennies speedily showed signs of distress, and changed colour, as they generally do, upon the most trifling cause. Instead of dark brown or black, their bodies appeared of a yellowish tint, spotted with white. Such a change was lovely to the eye, but, alas! it was-- 'The loveliness in death, Which parts not quite with parting breath.'