Amongst the Crabonides is a foot reversing all ordinary rules, belonging to the Mellinus, a sand wasp. Here the pulvillus is a large sucker on the apex of the claws (Fig. 10), instead of between them or under them. There is a reason good for this; the Mellinus provisions her nest with living flies, and a big blue-bottle by no means suffers himself to be quietly dragged into the dismal den where voracious young grubs await it; a fierce battle ensues, and even when so far overcome as to yield, and go struggling down, I can understand how useful to the Mellinus these suckers on the knuckles may be, in a difficult descent wrestling with its victim.

The legs of the tenthredo or saw-fly are easily mounted, being naturally transparent, and are particularly useful for examination of the joints; not only can the ball and socket between the tibia and tarsi be observed, but the muscular ligaments are often perfectly discernable in a well-mounted specimen (Fig. 11). The spurs, however, constitute its beauty, hanging in lobes from each joint of the tarsi. These little organs inosculate each in an appropriate socket, and have a degree of motion; they are also provided with a kind of sucker or pulvillus, which assists the insect in climbing and clinging to the twigs when the abdominal muscles are in full play during the preparation of its nest. Observe the position of its body upon an upright rose twig or gooseberry branch, the working of its saws with double-action blades, the whole frame quivering with exertion, and kept steady by these adhesive tarsi.

In May and June these saw-flies are common in every garden, and may be caught in the act of preparing the furrow from whence so many little hungry green larvæ will issue forth to desolate our fruit-trees.

Yet the Hymenoptera, as a class, are the ablest and best friends of man, and we may look gratefully as well as admiringly at the tiny feet. The honey-bee is an universal favourite; I never heard it maligned but once, when a crabbed old Cockney, who had retired to his country box, adjoining our residence, sent in a note requesting us to remove our bees, as they quite spoilt his (the Cockney's) flowers. But the rest of the tribe are not sufficiently appreciated, nor the immense importance of such avengers as the ichneumons and the Sphecides in keeping down hosts of caterpillars. What should we do with the larvae of the Pontia brassica if we had not the busy little Microgaster to stop their increase with her own maternal instinct. These small caterpillars, like many others, eat daily twice their own weight of leaves, as if an ox, weighing sixty stone, were to devour every twenty-four hours three-quarters of a ton of grass; and when we remember that each of those innocent-looking white butterflies, flitting over the cabbage-bed,

will deposit 1,600 eggs, we have reason to be grateful for the little friend whom God has sent to keep in check the voracious depredators; twenty-five out of every thirty caterpillars are destroyed by it. We all know the pest of our rose-trees, the little aphides, one of which in five generations is the progenitor of 5,901,900,000 descendants! These are followed persistently by the small ichneumon, Aphidius avena, and destroyed.

Does not the farmer tremble when in a July evening he sees the yellow cecidomyia hovering over the wheat ears? If he looked closer, he would see a small black ichneumon (Platygaster) following the track of the midge, and quietly dropping its own egg in the newly-hatched larvae, which will stop further mischief for this time.

The clover-worm hides in vain in the legume of the plant, and the wire-worm in the earth. The hymenopterous enemy finds out the vulnerable spot, and saves us from our unseen and often unsuspected foe. Pompilius and Pimpla manifestator keep down spiders and various voracious grubs, whilst the much abused wasp rids us of innumerable flies.

THE PRECESSION OF THE EQUINOXES, AND
APPARATUS FOR ITS IMITATION.

BY THOMAS W. BURR, F.R.A.S.

THE places of the fixed stars are necessarily designated by two co-ordinates, and those generally used are known as Right Ascension and Declination.

The former is the distance from a fixed point in the heavens, called the First Point of Aries, being one of the two places where the equinoctial and ecliptic cut one another; such distance being measured from west to east along the equinoctial, and reckoned either in 24 hours or 360 degrees. The two points of intersection of the circles called the ecliptic, or the sun's apparent path in the heavens, and the equinoctial, or earth's equator projected to the celestial vault, occur in the signs of the zodiac, Aries and Pisces; and the intersections or nodes mark the first points or beginnings of these signs. The nodes are also called the equinoxes, because when the sun is situate in either of them, the days and nights upon the earth are equal. The other co-ordinate Declination is the distance of a star from the equinoctial towards either the North or South Pole of the heavens, measured in degrees only, and is distinguished as north or south declination. It is, however, by many

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