If we cannot collect this Beetle for ourselves--which we should endeavour to do, if possible--it may be bought of almost any dealer in what are called ‘aquarium requisites.’ But prices rule higher for Hydrophilus than for Dytiscus. Bateman says that this species is rarer than formerly, and that specimens cost from 1_s._ to 2_s._ 6_d._ a pair, ‘according to the dealer and the season.’ From this I gather that I must have gone to a shop where the prices were reasonable, for I have never paid more than 6_d._ for a Hydrophilus, and then have been allowed to pick out a male. At the same shop I have paid 2_d._ for Dytiscus. [Illustration: FIG. 29.--Great Water Beetle. _a_, male; _b_, female; _c_, larva; _d_, pupa.] In keeping this Beetle we shall need a larger vessel than was required for Dytiscus. (In both cases the aquarium should be covered, for if food be scarce, and sometimes for other reasons, both these Beetles may take to flight.) The aquarium should be well supplied with growing water-weed, but none that is choice or valuable should be put in, for in moving about over the weed the animal will damage almost if not quite as much as it eats. This difficulty can be easily got over by supplying it with anacharis, water-crowfoot, milfoil, or any other common plant that grows rapidly and is easily procurable. The only specimen that I have taken myself was captured a few miles north of London. It exhibited a strange instance of depraved appetite. In the large tank into which it was put were growing vallisneria, frog-bit, and water-crowfoot in plenty. These it was never seen to touch. The tank, at one time, had been used for newts, and floating on the surface was a piece of virgin cork. It had served the former inmates as a kind of island continent, and had never been removed. To the under side of this the Beetle would moor himself, head downwards, and nibble away, as if cork were the natural diet of a British Water Beetle. In a few days the Beetle died. It was put into spirit, and soon after became the subject of a post-mortem. But its strange diet was not the cause of its death, which was sufficiently accounted for by injuries inflicted before its capture, probably by a larval or an adult Dytiscus. It would be mere waste of time to go over this Beetle and describe it point by point, as was done with Dytiscus. If what was there written was of any value, readers will be able to apply for themselves the method laid down. There are, however, some points of difference to which it will be well to invite attention. It is a good plan to lay specimens of these Beetles side by side for comparison. Hydrophilus is the larger of the two; and differs in colour as well as in size. Its hue is black with an olive tinge; and in certain lights a blue-black metallic gloss may be seen on the outer margins of the wing-cases. These are marked with faint longitudinal lines, and each bears three rows of dots running in the same direction.