ELEVENTH ORDINARY MEETING.

ROYAL INSTITUTION, March 19th, 1866.

J. A. PICTON, Esq., F.S.A., PRESIDENT, in the Chair.

The minutes of the last meeting were read and signed.

The Rev. John Sephton, M. A., was duly elected an ordinary member of the Society.

The following communication was then read:

OBSERVED FACTS IN THE NATURAL HISTORY OF THE CHIRONOMUS PLUMOSUS.

BY ALFRED HIGGINSON, M. R. C. S.

DURING the summer months of 1865 (say from May to October) I noticed the prevalence of red worms in a large earthen water-pot in my garden. These worms, the larvæ of the Chironomus Plumosus, attain a length of about one inch. They pass their time chiefly in tubes formed of mud and mucus, which they build on the sides of the pot, or on any object contained within the vessel. If left dry for any length of time, they quit the tubes, and swim for a time in the water. Their mode of progression is curious: the head and tail are brought together, and then immediately reversed; so that the appearance in the water is like a constantly repeated figure of 8, the impression of one circle remaining on the eye till the other is produced. These larvæ exhibit under the microscope powerful jaws, consisting of two upper mandibles and one lower, capable of breaking down vegetable structures. I once saw what I thought a fierce contest between two of these larvæ, but on investigation found that each was entangled by the same fibre, and they were only struggling to escape therefrom.

At the tail end there are appendages, which serve the purpose of respiratory organs. There are two anterior and two posterior organs of progression, situated on the abdominal surface of the body, each having at its extremity a sucking disc, surrounded by numerous hooks, and capable of being retracted and protruded as required.

In this larva, as in that of the gnat described by Dr. Carpenter, the circulation of the blood may be seen, propelled forwards through a dorsal vessel, and returning back

wards through the abdominal cavity, and surrounding all the viscera.

When fully grown, and transferred to a glass for observation, these larvæ are soon found to change into the pupa state, the skin and jaws being cast off, and forming a not uninteresting object for the microscope. This casting of the skin of the larva is said to take place in the gnat several times during its progress to the pupa condition, but it is not so in the Chironomus. The length of time occupied by the larva condition I believe to be variable, depending somewhat on the supply of food while in that state.

The pupa is a very different looking creature from the larva: shorter, and dark in appearance; tail thin, and hairy at the end; head large, and tufted with a respiratory apparatus. The agile movements of the larva are replaced by a bending of the body and an occasional quivering or struggling motion. The cases containing wings, and those containing legs, of the perfect insect, become defined, and at last, by a secretion of air within the pupa, it rises to the surface of the water. I have twice seen the insect make its escape, and the time required is less than I shall need to write its description. The ascent from the depths of the garden-pot being noted, it no sooner reaches the surface than the portion which rises through the water bulges and cracks, and the head and body of the perfect insect come quickly into view. The legs and wings are shot out almost at once, and the insect floats away a few inches on the water, resting on its feet, before it spreads its wings and soars aloft. It was on a Sunday morning that I saw this beautiful phenomenon take place, and certainly the escape of this light and joyous insect, from its dense medium and confined dwelling, into the free air and sunshine, might well typify the rise of man's immortal part into the light and presence of his Maker.

The little voyager, however, has not done with this world.

The male Chironomus has large antennæ, and the tail is bifid, or furnished with forceps at the extremity. The female has little or no development of antennæ, and the tail is unarmed. Now about the eggs: I have seen the insects constantly hovering about the water-pot, and more than once have observed one at the edge of the water, resting, for some time, with its tail downwards. On examining the spot, I have found attached to the vessel a capsule of eggs, such as I will now describe. A gelatinous-looking mass, cylindrical in form, not exceeding three-quarters of an inch in length and one-eighth in diameter, adheres by one extremity to the vessel, the other end being free, and of a rounded form. It is easily compressed on a microscope slide, and found to have a structure of its own, namely, two bands or cords, running through its long diameter, and lateral septa, rather numerous, at right angles to these. In the divisions thus formed, eggs are found to the extent of two hundred or more. These eggs at first appear filled with slightly amber-coloured granular matter, but after a time life is evidenced by movement, and even circulation; the animal at last makes violent and repeated exertions. The sac bulges and gives way, and the larva, a perfect miniature of what I have already described, escapes from the egg. The empty shell may be found long afterwards. The egg is lengthened and flattish, like the seed of a melon, but scarcely visible without a lens. That these larvæ, from the first, feed on vegetable substance, was evident to me, from finding that a few blades of grass inserted into a wine-glass containing them were before long denuded of all their green structure, and the strong fibre alone remained unconsumed.

As already stated, I believe the period of the larva's change into the pupa to depend partly on its power of obtaining food.

At first I imagined this insect to be the gnat, which it a

good deal resembles; but the increasing discrepancies convinced me that I must look beyond the Culicidæ, which only comprise the gnat and mosquito. The Tipulidæ, or Longlegs, equally belong to the order Diptera, but are very numerous, eighty species being said to belong to the genus Chironomus. The name seems derivable from the Greek Chironomeo, to gesticulate, the insect having the curious habit of carrying the front legs, pointing forwards, both in flying and walking. This position may have reference to its mode of catching its prey, it being said to feed on the Aphis.

Professor JEVONS then gave a "Preliminary Account of certain Logical Inventions," the Logical Abacus and Logical Machine.

He began by remarking upon the aids which we constantly use in thinking and calculating. Words were nothing but mechanical signs, used to represent our thoughts; and philosophers were not without excuse when they doubted whether any true reasoning could be carried on without the use of language. The very name calculation pointed to the use of pebbles in reckoning; and the similar use of fingers in assisting our remembrance of numbers was the origin of the decimal system of numeration which exists in all civilised nations. Every one must have felt how laborious and uncertain was mental arithmetic, and how great a relief was the use of any sort of signs. He then described the abacus or arithmetical board, which had been used by a great many nations, such as the Greeks, Romans, Germans, French, and especially the Chinese. It consisted usually of a small square frame, with several horizontal wires strung with beads, which could be varied in order and made to represent various numbers, so as to facilitate calculations. The possibility of calculating by machinery had been proved by the

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