This puts the matter beyond doubt, if any before existed. I at once wrote to Mr. Tegetmeier to let him know that my experiments had, unknown to me, been anticipated, long ago, by Mr. Sowerby. Had he rescued his Planorbis shell, it would have compared very well with those forwarded to the Field office in 1893. They had been exhibited at the Malacological Society, and no one was able to solve the mystery of their mutilation. This shows, to quote the Field[10] on the subject, ‘how easily statements that have been recorded may subsequently be overlooked and entirely forgotten.’
To return to our Beetle. The male is a handsome creature, from an inch to an inch and a quarter long, clad in olive-green, bordered with yellow, and exceedingly active. His mate is smaller, more soberly clad in brown, without the yellow markings, and the wing-cases are more or less furrowed.
The first thing to notice is the shape of the body, oval and smooth, offering no resistance to the water. The hind pair of legs are flattened and fringed with hairs, so as to make capital paddles. In swimming the right and left legs are moved together.
Now, though this Beetle lives in the water, it is made, so far as concerns its breathing apparatus, after the fashion of a Land Beetle, and consequently is compelled to come to the surface pretty frequently for a supply of air, which it obtains in this wise. Directly it ceases paddling it floats to the top of the water; and as the head is heavier than the tail the latter projects a little above the surface. Then the wing-cases are raised, and air flows in under them to the breathing holes on each side. The operation is not a long one, and as soon as it is over the Beetle is ready for another ramble round his dwelling-house.
But if we do not supply our captive with food that he may take for himself, it is only right that we should feed him, which may be done at intervals—say, every other day. ‘Little, and often,’ is an excellent motto to guide us in our feeding; and though its adoption may entail some trouble, it will be more than compensated by the success that will attend our endeavours to keep the inmates of our aquarium in good condition. And the operation of feeding our Beetle will show us that he has some capital sense-organs, which are of as much, if not of more, use to him than his eyes.
He is a flesh-eater. Let us take a small piece of meat or fish in a pair of forceps, or stuck on a pointed stick, and hold it at a little distance from his great eyes. The chances are that he will not see it. Even if we put it in front of him, he is quite likely to disregard it, for he has nothing corresponding to a nose, with which he may smell. From his head there spring a pair of long feelers—the antennae—and by means of these we will let him know that his dinner is ready. That is effected by drawing the food along the side of one of the antennae. The creature undergoes a sudden change. Till the antenna was touched with the food he was resting on his swimming legs. But in a moment down goes his tail and up goes his head, he stretches out his raptorial legs, and clutches wildly at the forceps or stick, as the case may be, holding so tight that he may be dragged round and round the glass vessel. Let go he will not, of his own accord; and it would be a difficult matter to shake him off. Similar experiments may be tried with other Beetles, and the result will be to impress on the mind the fact that the feelers are capital sense-organs.
If we are to turn our Beetle to the best account, we shall need to handle him. It may be inconvenient to wait till he dies, so we will kill him quickly and painlessly by plunging him into boiling water, and he may be preserved by putting him into a tube containing about equal parts of water and spirit, or a five per cent. solution of formalin.
Dissections should properly be made under water. The Beetle should be fastened, back upwards, to a piece of cork weighted with lead, and placed in a deep saucer, or dissecting dish, and covered with water. But a good deal of rough dissection, as is ours, may be done in air, and the Beetle may be fastened to any convenient piece of board, or even held in the palm of the left hand. Very little practice is needed to run over the external parts of a large Beetle in this manner.
Fig. 17.—Outline of Dytiscus (male). a, antenna; b, maxillary palp; c, eye; d, fore-leg; e, thorax; f, middle leg; g, elytron; h, suture; i, hind leg; j, claw; k, tarsus or foot; l, tibia or shank; m, femur or thigh; n, first three joints of foot, widened into a plate with suckers beneath.