were well and carefully washed in warm water, dried before a fire, and, after scratching the description or name on a corner, varnished with the usual solution of amber in chloroform.

The subsequent operation of printing is so easily performed, and has been so fully described by persons of more experience than myself, that any further allusion to it will be needless.

Appendix.

Besides the pictures taken in America-which are almost valueless as moon maps, as the sides are reversed in the copying from the daguerreotype plate upon which they were originally taken, the moon has been photographed by Professor Phillips, Father Secchi, MM. Bertsch and Arnauld, several Liverpool photographers, and Mr. Hartnup and myself. It is interesting and instructive to compare among themselves the means employed and the time occupied in taking the impression on these several occasions.

Professor Phillips's telescope has a sidereal focus of 11 feet, and an aperture of 6 inches; consequently the brilliancy of the moon's image in its focus is augmented 26 times over what she appears to the naked eye. The average time occupied for the collodion plate to receive the impression was about 3 minutes.

Father Secchi's telescope having a sidereal focus of 18 times its aperture, the moon's image was intensified 37.8 times, and the time required for the impression was an average of 6 minutes.

M. Porro's glass of 49 feet sidereal focus and 20 inches aperture, gave a moon image 12.3 times brighter than she appeared to the naked eye, and the average time of taking the picture was 17 seconds.

Mr. Hartnup's telescope being 12 feet focus and 8 inches aperture, augments the intensity of the moon's image at its focus 35 1 times. The time which was required for the photograph of our satellite to be taken, on the occasion of the meeting of the British Association at Liverpool in 1854, was about 2 minutes; and under the same circumstances we ourselves succeeded in obtaining perfect and intense negatives in 4 seconds. These, however, were taken under very unfavourable circumstances, the temperature being below the freezingpoint, and the moon at a considerable distance from the meridian,

which necessarily caused both a diminution of the light and also a diminished sensitiveness of the collodion film.

The rapidity with which the above pictures were taken may be better understood by comparing them with those of terrestrial objects under similar circumstances. According to Herschel*—

"The actual illumination of the lunar surface is not much superior to that of weathered sandstone rock in full sunshine. I have frequently compared the moon setting behind the grey perpendicular façade of the Table Mountain, illuminated by the sun just risen in the opposite quarter of the horizon, when it has been scarcely distinguishable in brightness from the rock in contact with it. The sun and moon being nearly at equal altitudes, and the atmosphere perfectly free from cloud or vapour, its effect is alike on both luminaries."

Thus by comparing the Liverpool object-glass as to power with our ordinary camera lens, its focal length being nearly 19 times the aperture, and the moon's image being copied by its means in 4 seconds, we find that it is equivalent to copying sandstone illuminated by the sun in 4 seconds with a lens 4 inches focus and a little less than inch diaphragm; or with a compound lens having an aperture of one inch, and the same focal length, in a quarter of a second.

II. "Researches on the Reproductive Organs of the Annelids." By THOMAS WILLIAMS, M.D., F.L.S., Physician to the Swansea Infirmary. Communicated by THOMAS BELL, Esq., F.R.S., P.L.S. &c. Received December 30, 1856.

(Abstract.)

In this paper the author seeks to establish the following general proposition, viz. that there prevails throughout the Actiniada, Echinodermata, Rotifera and Annelida, a special organ, which, under different phases, subserves different functions, which is essentially identifiable under every modification, reducible to the same type, and which constitutes the root of the Reproductive system in these families. To this special organ he proposes to apply the provisional

*Herschel's Outlines of Astronomy, page 249.

name of the " segmental organ* *." In the chambers which are enclosed by the vertical dissepiments dividing the body of Actinia, convoluted tubular cords are contained which support the generative structures. It has not yet been proved whether the internal ends of these tubules open directly into the perivisceral chamber. These cords and their appended structures in the Actiniadæ, constitute the type of a system of organs the prevalence of which throughout the Echinodermata, Rotifera and Annelida can, he believes, be clearly and satisfactorily proved. In the present memoir, however, the author proposes to confine his demonstrations to the anatomical varieties which the segmental organ presents in the class Annelida, contenting himself with merely in a passing manner pointing out the fact that the several variations of form, structure and number which this organ exhibits in the several genera of this class, are represented by similar variations in the different genera, especially of the class Echinodermata. He hoped to show that under very numerous apparent varieties, the essential unity of the segmental organ within the indicated limits can be convincingly established.

Upon this organ, under different circumstances, there devolve one or two or even more functions. Sometimes it is used as a simple discharge tube, conveying externally in a direct manner the fluid of the general cavity of the body. This variety is exemplified in the segmental organs which are distributed, in the genera Lumbricus and Nais, throughout all that part of the body which is situated posterior to the Reproductive band. In this latter region two or more of these organs are so modified as to become the basis whereon is developed the generative structures.

Here the author enters upon a minute account (illustrated by figures) of the history of this organ in Lumbricus and Nais, showing the changes of outward form which it undergoes in several species of these genera.

He points out in this place that the segmental organ, as it occurs in Lumbricus and Nais, is paralleled by the so-called water-vascular system of the Rotifera: as in the former so in the latter, the ciliated tubes communicate openly with the general cavity; in both, the cur

* While he is convinced that the identity of this organ might readily be traced throughout other families of the lower Invertebrata, he will not permit himself at present to indulge in any wider generalization than that stated in the text.

rent raised by the cilia travels from within outwards; and he contends that the reproductive structures are ingrafted upon, or developed from one, two or more of the ciliated tubes in the Rotifera, as from the segmental organs of Lumbricus and Nais.

Arenicola and Terebella form a group in which the segmental organ deviates in a remarkable apparent manner from that of Lumbricus and Nais. It forms a series of elongated sacculi, which are attached to the ventral wall of the general cavity on either side of the median line. Each sacculus, although single at its distal end, is divided at its attached end into two tubular limbs, one of which communicates directly with the exterior, while the other opens immediately into the general cavity of the body. Through the latter limb the ova and sperm-cells are introduced into the perivisceral chamber, while in the reverse direction the fluid of this chamber is discharged externally. The author has never been able to discover how the germ- and sperm-cells (respectively in the female and male) escape out of the general cavity. But he trusts that he has given a new and satisfactory demonstration of the mode in which they enter that cavity. The genera Arenicola and Terebella comprehend the only Annelids in which the germ-elements in the female, and the spermcells in the male, are ushered into, and are required to sojourn for a season in the fluid of the general cavity of the body.

He indicates in this place that the segmental organ of the Sipunculida (amongst the Echinoderms) corresponds both in its structure and relations to that of Arenicola and Terebella, with this difference only, that in the latter a special and peculiar development of the blood-vascular system occurs around and in the vicinity of the segmental organ, whereas in the Sipunculidæ this system scarcely exists and never receives any enlargement. The segmental organs in the genus Synapta stand in an intermediate position between those of Holothuria and those of Sipunculus. In Synapta one or more organs remain in the condition of simple discharge tubes,' while others become developed into the Reproductive structures.

The segmental organs of the Hirudinaceæ are next described. The author adheres almost in every detail to the results published by him in 1851 in the Transactions of the British Association, with reference to the reproductive system of this family of Annelids. In the present memoir he records the results of new and carefully conducted dissections, which prove that in the Common Leech, the Sea-leech,

and probably in the genus Clepsina, there is situated an organ on either side of the ventral median line, which is repeated in every ring of the body, and which in this family is the true ovigerous apparatus, the testes constituting a separate and more medianly disposed series of glandular bodies, whose homologies he has not yet satisfactorily determined.

The so-called "respiratory sacculus" of Dugès he now looks upon as the process of the ovario-segmental organ, by which a communication is established between the latter and the general cavity of the body, and by which the fluid of this chamber escapes externally. All the Hirudinacea are androgynous.

Under the Nereid group is included in this memoir, the genera Nereis, Aricia, Phyllodoce, Nephthys, Syllis and Nerine. The segmental organ in these families is specially described and figured. In all, the sexes are seated on separate individuals. In no single instance is the general cavity rendered subservient to the incubatory process. In all, the general circumference of the organ is lobulated and irregular, entering the hollow bases of the cirrhi and blended most intimately with the blood-vascular system.

Glycera and Cirrhatulus the author classes together, on account partly of the similarity of form and structure of the segmental organ, but especially because in both the blood-vascular system is completely and entirely wanting, its absence being compensated by the existence of a second order of pigment-carrying corpuscles in the cavitary fluid. These genera are unisexual, and at no time are the germ- and spermelements introduced into the perivisceral chamber.

In this and the preceding groups the author has not succeeded in discovering the mode in which the segmental organ opens into the general cavity; but from the fact that it has a looped arrangement, supported on two tubular limbs, he is quite convinced that an opening into this cavity, for the purpose of giving direct outlet to its contents, does really exist. This conclusion is fortified by the analogy of the form under which the organ exists, in the Nereid group in general.

The Nemertine Annelids are then examined. The author recalls the results of his researches as published in his 'Report' on the Annelids in 1851. His renewed investigations have confirmed the statements which he then put forth. He still contends that what M. Quatrefages has described in these worms as the orary is a great