* Dr. Grant's figure of the nervous system as he supposed it to be arranged in Cydippe pileus, is given in a preceding page, fig. 57, 2.

(322). From the researches of Will1, it would appear that these Acalephs are hermaphrodite, the generative apparatus consisting of elongated utricles, the testes being situated on one side and the ovaria on the other. Both sets of organs are described as having a nodulated appearance, and from the nodulated part of each passes off an excretory duct, which runs towards the mouth; but the terminal openings of these canals have not been made out. In Professor Grant's description of Cydippe pileus, of which a figure is given above (fig. 58, l), the ovaries are said to consist of two lengthened clusters of small spherical gemmules of a lively crimson-red colour, extending along the sides of the alimentary canal. It is evident, therefore, that further knowledge relative to this department of the economy of the Beroes is still a desideratum in science.

(323). The Cestum Veneris (fig. 59) is nearly allied to the Beroe in the arrangement of its nutritive apparatus, notwithstanding the difference of form observable in these Ciliograde Medusae. In Cestum, the digestive cavity, which is exceedingly short in comparison with the length of the animal, passes transversely across the body in a straight line from one side to the other, as represented in the engraving; but the details of its structure, and the nature of the vessels arising from it, will be best understood by a reference to the enlarged diagram of these parts given in the next figure (fig. 60.) The mouth, i, is a rhom-boidal depression, seen near the centre of the body, between the two lateral rows of locomotive cilia, which extend from one end of the animal to the other. From the mouth arise two tubes, j j, which terminate in a globular cavity common to both (these would seem to constitute' the digestive apparatus); and a straight narrow tube, o, prolonged to the opposite margin of the body to that which the mouth occupies, may be regarded as an intestine through which the residue of digestion is discharged. From around the oral extremity of the stomach, and from the globular cavity in which the two principal canals terminate, arise vessels, t t t, which diverge so as to form a cone, at the base of which they all empty themselves into two circular canals, one surrounding the mouth, and the other encircling the anal aperture, which precisely correspond with the vascular rings already described in the Beroe; and, from these, four long vessels, or branchial arteries as they might be termed, p p, q q, are prolonged beneath the four ciliated margins all around the body.

But besides these four nutritive vessels, two others, x x, arise from the anal ring, which run inwards towards the centre of the animal, and afterwards assuming a longitudinal direction, serve to distribute nourishment to the median portions of the animal. The caeca, or blind tubes, n n, appended to the intestine, may possibly furnish some secretion useful in digestion, although perhaps we are scarcely warranted in saying decidedly that they are biliary organs*.

308 Ciliograda 75

Fig. 59.

* Mem. sulla steria e anatomia degli Animali senza Vertebre, torn. iv. p. 12. 1 Horre tergest. p. 38. tab. 1. figs. 22, 23.

(324). Extraordinary as must appear the powers which the Acalephae possess of seizing and dissolving other creatures apparently so dispro-portioned to their strength and the delicate tissues which compose their substance, there are other circumstances of their history equally remarkable, which, in the present state of our knowledge, are still more inexplicable. If a living Medusa be placed in a large vessel of fresh sea-water, it will be found to secrete an abundant quantity of glairy matter, which, exuding from the surface of its body, becomes diffused through the element around it so copiously, that it is difficult to conceive whence materials can be derived from which it can be elaborated. Of the origin of this fluid we are ignorant, although certain glandular-looking granules, contained in the folds of the pedicle, have been looked upon as connected with its production.

Alimentary apparatus of Cesium.

Fig. 60. Alimentary apparatus of Cesium.

* Delle Chiaje, Memorie per servire alia storia degli Animali senza Vertebre del regno di Napoli. 4to, 1823-1825.

(325). We are equally at a loss to account for the production of the irritating secretion, in which the power of stinging seems to reside; but it is observed that the tentacula seem to be more specially imbued with it than other parts of the body. Perhaps the most remarkable property of the Acalephae is their phosphorescence, to which the luminosity of the ocean - an appearance especially beautiful in warm climates - is principally due. We have more than once witnessed this phenomenon in the Mediterranean; and the contemplation of it is well calculated to impress the mind with a consciousness of the profusion of living beings existing around us. The light is not constant, but only emitted when agitation of any kind disturbs the microscopic Medusae which crowd the surface of the ocean: a passing breeze, as it sweeps over the tranquil bosom of the sea, will call from the waves a flash of brilliancy which may be traced for miles; the wake of a ship is marked by a long track of splendour; the oars of your boat are raised dripping with living diamonds; and if a little of the water be taken up in the palm of the hand and slightly agitated, luminous points are perceptibly diffused through it, which emanate from innumerable little Acalephae, scarcely perceptible without the assistance of a microscope.

All, however, are not equally minute: the Beroes, in which the cilia would seem to be most vividly phosphorescent, are of considerable size; the Cestum Veneris, as it glides rapidly along, has the appearance of an undulating riband of flame several feet in length; and many of the larger Pulmoni-grade forms shine with such dazzling brightness, that they have been described by navigators as resembling "white-hot shot," visible at some depth beneath the surface. This luminousness is undoubtedly dependent upon some phosphorescent secretion; but its nature and origin are quite unknown.