II. "An Account of the two Methods of Reproduction in Daphnia, and of the Structure of the Ephippium."" By JOHN LUBBOCK, Esq., F.G.S. Communicated by CHARLES DARWIN, Esq., F.R.S. Received December 22, 1856.

(Abstract.)

In this paper the author describes the male organs and the structure of the Ephippium in the genus Daphnia, and the double method of reproduction by agamic and ephippial eggs. The author calls the non-ephippial eggs agamic, but it is possible, though not probable, that the ephippial eggs may be agamic also. In the male Daphnia there are two small papillæ above the posterior claws, but on the ventral side of the anus, and on these being compressed, two streams of minute rod-like bodies, with movements so gentle as to be scarcely visible, will be seen to issue, one from each papilla. Nothing similar has ever been observed in the female; nor has any other sort of spermatozoa ever been met with. These male organs have never been described before.

The author then proceeds to describe and figure the two sorts of eggs in their earlier stages, which have not yet been mentioned by any naturalist. The ephippial eggs differ from the agamic in their determinate position and number. As a general rule, that is to say, in seventeen cases out of twenty-three, the author has remarked that ephippial eggs commence and are developed to a certain point.

The development is as follows. One of the ovarian cells, always at the posterior part of the ovary, swells a little, and becomes a germinal vesicle; round it are deposited a number of brownish granules, while the other cells which may at first have existed in the same ovarian mass cease to be visible. The deposition of dark granules, in thirty-seven cases out of forty, after proceeding to a certain point, ceased, and the embryo egg gradually disappeared. In the other three cases it increased, and at length formed a dark mass on each side of the intestinal canal. The author in two cases observed the ephippial eggs pass from the ovary into the receptacle.

The ephippium has been described by Strauss with considerable accuracy, but he has been more or less misunderstood by all subsequent writers on the subject, and no one has explained the homologies or connexions of the inner valve. The ephippium itself is

a locally altered portion of the carapace; the outer valve of the ephippium being a part of the outer layer of the epidermis, and the inner valve the corresponding part of the inner layer. In consequence of this arrangement, the inner valve of the ephippium, containing the ephippial eggs, is not attached by the hinge to the outer valve, as has been generally stated, but actually lies at first in the receptacle formed by the new carapace. The ephippium is cast with the rest of the skin, from which however it soon becomes detached, and continues to form an efficient protection to the eggs until they are hatched. These eggs probably require to be fertilized, but this fact is not completely proved. With one exception, whenever the author observed ephippia, he could also find males; and, generally speaking, the numbers of each were in proportion to one another. Impregnation is not, however, absolutely necessary to the production of ephippia, as the author has now in his possession three ephippia, formed by isolated females. It remains to be seen whether young will be developed from these or not.

The early stages of the agamic egg are very similar to those of the ephippial egg, and consist of the enlargement, in the front part of the ovary, of one of the ovarian cells, which then becomes a germinal vesicle, and the deposition round it of granules, with the addition in this case of oil-globules. This process continues, the other two or three cells which may have existed in the same ovarian mass gradually disappear, and there is thus formed an egg-like mass, consisting of a germinal vesicle, minute dark granules, and large oil-globules. When the growth is nearly completed, the vitelline membrane is added. This is at first very delicate, but after deposition in the receptacle soon becomes hard. The ovarian eggs of Daphnia, as well as those of Cypris, never contain round masses like those of Aphis and Musca; but after their entry into the receptacle, yolk masses are found, homologous with those present at the corresponding periods in Phryganea*. The eggs when laid are about 30 of an inch in diameter; they gradually become 36, when the vitelline membrane splits and falls off, and the young animal is hatched. Far, however, from resembling its parent at this time, the young Daphnia

* The round balls described by Herold in the ovarian eggs of Bombyx, appear to be of a different nature, and homologous with the Nahrungsdotter mentioned by Carus in spiders' eggs and the oil-globules of Daphnia.

is a spherical bag, inside which the formation and development of the new organs is rapidly progressing*. Instead therefore of undergoing no metamorphosis, the young Daphnia only assumes the wellknown characters of the genus after the first changes of skin. The author proceeds to compare this phenomenon with a similar one observed by Mr. Spence Bate in Gammarus, by Prof. Huxley in Mysis, by Dr. Cohn in Sphæroplea, in many Annelids, and in the interesting entozoon Monostomum mutabile. The young Daphnia attains a length of 025 inch before it leaves the receptacle of the mother, but the length of time during which it remains therein varies according to the temperature. The author has never met with an exception to the rule noticed by preceding writers, that unisexuality is characteristic of an agamic brood.

It follows from these observations, that the self-fertile Daphniæ are certainly true females, and that the reproductive bodies more nearly resemble eggs than gemmæ in their origin and development. Hereafter, however, it may be convenient to give a separate name to those egg-like bodies, which are fertile without impregnation, but for the present they must be called eggs.

The author then gives a list of the instances of Parthenogenesis which, so far as he knows, are recorded among the Articulata. Finally, he expresses the belief that the careful consideration of these cases, and of the facts now recorded as to Daphnia, and the still more wonderful observations recently detailed by Siebold in regard to Apis (if these latter are confirmed), must surely remove all lingering doubts as to the identity between eggs and buds; and remarks, that if Prof. Huxley's definition of "individual" and "zooid" is to be adopted, it will be impossible to assert of any Daphnia or Moth, whether it is the one or the other, and the hive-bee will have to be considered as an hermaphrodite, a species without male individuals.

Under these circumstances, the author suggests that it would be more convenient to continue, as heretofore, to call the individual of any species that which is individualized, even though in this case the individuals of one species will not always be homologous with those of another.

*It is worthy of notice, that the back fold indicating the divisions between the head and body is opposite the line between the mandibles and the first pair of maxillæ, which latter appear therefore to belong to the body, as Zaddach also asserts, and not to the head.

III. "On the Thermo-electricity of Ferruginous Metals, and on the Thermal Effects of stretching Solid Bodies." By J. P. JOULE, F.R.S. Received January 29, 1857.

The experiments on the above subjects were made with a thermomultiplier placed in the vacuum of an air-pump. Its sensibility was such that with the junction antimony and bismuth, a thermometric effect not greater than of a degree Centigrade could be estimated. In determining the thermo-electric position of the metals, it was necessary to increase the resistance of the instrument a hundredfold, by placing in the circuit a coil of fine wire. In thermo-electric arrangement steel was found to be nearer copper than iron was. By hardening, steel was raised almost to the place of copper. Cast iron was found to surpass copper; so that the junction cast iron and copper is reverse to that of wrought iron and copper, and the arrangement cast iron and wrought iron is much more powerful than copper and wrought iron. A new test of the quality and purity of ferruginous metals is thus indicated, which will probably be found of value to the arts.

The experiments on the stretching of solids showed, in the case of the metals, a decrease of temperature when the stretching weight was applied, and a heating effect when the weight was removed. An iron wire of an inch in diameter was cooled of a degree Centigrade when stretched by a weight of 775 lbs. Similar results were obtained with cast iron, hard steel, copper, and lead. The thermal effects were in all these cases found to be almost identical with those deduced from Professor Thomson's theoretical investigation, the par

t

ticular formula applicable to the case in question being II= × Pe, where H is the heat absorbed in a wire one foot long, t the absolute temperature, J the mechanical equivalent of the thermal unit, P the weight applied, and e the coefficient of expansion per 1°. With gutta-percha also a cooling effect on extension was observed; but a reverse action was discovered in the case of vulcanized indiarubber, which became heated when the weight is laid on, and cooled when the weight was removed. On learning this curious result, Professor Thomson, who had already intimated the probability of

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a reverse action being observed under certain circumstances with india-rubber, suggested to the author experiments to ascertain whether vulcanized india-rubber stretched by a weight is shortened by increase of temperature. Accordingly, on trial, it was found that this material, when stretched by a weight capable of doubling its length, has that length diminished by one-tenth when its temperature is raised 50° Centigrade. This shortening effect was found to increase rapidly with the stretching weight employed; and, exactly according with the heating effects observed with different stretching weights, entirely to confirm the theory of Professor Thomson.

February 5, 1857.

The LORD WROTTESLEY, President, in the Chair.

THE BAKERIAN LECTURE was delivered by MICHAEL FARADAY, Esq., F.R.S., "On the Relations of Gold and other Metals to Light."

The Lecturer gave an exposition, illustrated by experiments, of the substance of a paper presented by him to the Society under the above title. The following is an abstract :

The author of this paper hopes that the undulatory theory of light, when more fully and perfectly developed, may aid in comparing local actions with those which take place at a distance, and even help towards the comprehension of the physical means by which the latter are carried on; and with that view he endeavoured, experimentally, to subject a ray of light to the action of particles, so small in size as to have an immediate and near relation, not only to the undulations of light, but even to the far smaller motions of the parts of the ether, which are supposed to produce, by their joint and successive action, the light-wave. His hope was, that by choosing particles of a fitting substance, experimental results might be obtained which, in the hands of the mathematical philosopher, might aid in perfecting the theory; and for this purpose gold was selected, because of its high optical