centre of that line, where they form a nearly equilateral triangle, with one angle N. The N.W. side of this area is bordered by a long dark valley, extending S.W. 37 miles, and dividing it from a system of small parallel chains, whose highest summit, , attains about 2600 feet. This mountain, already mentioned in p. 371 of our last number, must be looked for just S.S.W. of the little but conspicuous crater c, the only one at once S.W. of Copernicus and S.E. of Stadius; it must also stand very near the N.E. end of the bright streak which divides Rhaeticus in the Full Moon (p. 216, antea). Of the parallel ridges they say, "these mountains are very dark, and here, in the Full Moon, a large blackish spot shows itself," in which they are unconsciously describing the W. part of their vainly-sought Rhaeticus of Riccioli, the other portion seeming to be the "long dark valley" just described. There appears little doubt that in this parallelism may be found the "rampart-work" of Gruithuisen, the regular arrangement of which would probably repay a search; at the other end of the streak dividing Rhaeticus, and consequently near the S.W. angle of their hill-triangle to the E. of it, they place a little summit e. They remark that while the dark mountains continue so in full illumination, the triangle is brighter, 3° to 34° of light, and e has "exclusively a brilliancy of 7°, which it does not lose even in the neighbourhood of the terminator, an anomaly which is so much the more remarkable because it otherwise is not distinguished, either through form or elevation, from the rest, several of which overtop it." I regret that Í did not notice this curious passage in time to compare it with the existing state of reflective power, but I have no recollection of such a spot when I was identifying Rhæticus, the notices of which are strangely scattered about in B. & M., and it must be left as an interesting subject of research for some of our readers.

E. of Gambart is a bright (8°) and conspicuous little crater A.

Reinhold (our 31) is a crater 31 miles in diameter, with strong terraces and a central hill at the N. end of a little ridge. The W. side of the ring is 9400ft., the E. 7000ft. above the interior. Schr. gives the former measure 8700ft., and makes the external height of the E. wall 1900ft. A mountain-ridge connects it with Copernicus, bending, as it were, round both the rings.

N.E. of Copernicus, we find a lofty tract which B. and M. call Mt. Carpathus, extending with its dependencies from E. to W. 280 miles. It includes Gay Lussac, a double crater already described in our p. 370: the smaller basin A is deeper, steeper, and brighter than its broader, and apparently more

ancient neighbour; a relation frequently obtaining in these configurations. Close S.E. of it our guides notice a dark spot in the Full Moon; an exemplification of our recent remarks. The ring of Gay Lussac is interrupted by a minute crater close to the companion-crater A; and they point out a curious arrangement here: three pairs of objects-A and this little pit-two summits (a) close together on the N.W. slope of the ring-and two others (8) on the E., make up respectively two equilateral triangles, with sides parallel and very close together, whose common centre coincides with that of Gay Lussac itself. The cleft proceeding from it has already passed under our review. The mountains E. are confused in arrangement, with no central axis; and are penetrated by valleys usually as luminous as the heights. Measurement is difficult from the way in which the shadows fall. One high promontory reaches 6300ft. Towards the E. extremity lies a considerable crater, Tobias Mayer, 22 miles in diameter. A summit of its W. ring rises 9700ft. above the cavity. Schr. pointed out that in consequence of its position on the mountain's flank, its E. side was much lower—he gave it but 2700ft. (short measure). It has a central hill, which from local colour appears large in Full Moon. S.E. of this the map shows a very minute crater in the depth; rather an unusual position. W. of the ring lies a conspicuous sub-crater, as it might perhaps be termed, Mayer a. The extremity of the mountains N.E. of Mayer rises to 4000ft.-Milichius, a small bright (8°) crater lies in a curiously-shaded region of the M. Imbrium (I), nearly S. of Mayer and E. of Copernicus. S.S.E. of this is another similar crater, Hortensius, very remarkable for its isolation, and the luminosity surrounding it, almost like a miniature streak-system. In a position forming a right-angled triangle with the two last objects the right angle being towards Copernicus-is a spot containing within the compass of less than 30 miles eight parallel ridges running nearly N. and S., and all pretty nearly of similar length and elevation.

Another step S.W. brings us from Hortensius to Reinhold again, and completes the circuit of a region where so much is seen, and so little is understood, of the wonderful works of God.

TRANSITS OF JUPITER'S SATELLITES.

Jan. 1st. I. egress, 5h. 11m.-Ditto shadow, 6h. 16m.— 5th. II. shadow ingress, 5h. 50m. II. egress, 6h. 34m.— 8th. I. shadow ingress, 5h. 53m. I. egress, 7h. 12m.12th. II. ingress, 6h. 29m.-15th. I. ingress, 6h. 54m.24th. I. egress, 5h. 45m.-Ditto shadow, 6h. 31m.-30th. II. shadow egress, 5h. 45m.—31st. I. shadow ingress, 6h. 8m.

OCCULTATIONS.

Jan. 6th. 48 Tauri, 6 mag. 9h. 20m. to 10h. 24m. y Tauri, 4 mag. 11h. 28m. to 12h. 33m.-30th. f Piscium, 6 mag. 9h. 56m. to 10h. 26m.

OUR FRESH-WATER PLANARIE.

BY W. HOUGHTON, M.A., F.L.S.
(With a Plate.)

ANYBODY who has occasionally gathered water-cress, or searched amongst aquatic weeds for objects for the aquarium, must be acquainted with certain small black or brown creatures, of an oblong form when at rest, soft, smooth, and flat, and about five lines in length and one and a half broad. These are two species, or, it may be, two varieties only, of Planarian worms. Probably the collector of objects for the aquarium sees in these animated black blotches very little to attract his attention, and he throws them aside; or if curiosity tempts him to bottle a few specimens for examination, he finds that he is able to make out very little of their structure, and sees scarcely anything to interest him in their habits; and certainly when we compare these fresh-water Planarice with other rare and exquisite forms of animal life, such a Cristatella, Fredericella or Plumatella amongst our fresh-water Polyzoa, or a Melicerta or a Stephanoceros amongst the Rotatoria, these little black dabs have small claims to beauty; nevertheless the large white species, Planaria lactea, with the pink arborescent ramifications of its digestive system, is by no means devoid of beauty, whilst the commoner black or brown kinds present many points of interest to the naturalist, both in their habits and anatomy. The Planaria, as their name imperts, are of a flattened form; the under surface of some of the species bears some resemblance to the foot of a gastropodous mollusc. In many parts of their organization the Planaria resemble the Flukes which inhabit the liver and other viscera of various animals, especially ruminants; but none of the Planaria are internal parasites, nor do they, like the Flukes, undergo a metamorphosis. They inhabit fresh and salt water, and are to be found on the leaves and stems of aquatic plants, and amongst the roots of the Laminaria, between tide marks. On the present occasion I shall confine my remarks to the fresh-water species, of which a great number have been described as occurring in France by Dugès who has published two very interesting memoirs on these animals.* In this country also, * See "Annales des Sciences Naturelles," Tom. xv. and Tom. xxi.

several kinds are found, of which Planaria lactea, P. torva, Polycelis nigra, P. brunnea are common everywhere in ponds, streams, and ditches. A favourite place of resort of these creatures is within the stems of Sparganium, whence they may be readily picked or scraped off with the point of a knife and placed in a bottle of water. Difficulties of dissection long prevented naturalists assigning to the Planaria their true place in the animal kingdom; Cuvier, following Müller, Linnæus, Pallas, and Lamark, placed them amongst the parenchymatous Intestinalia, or Trematode Entozoa (as the Flukes Distoma), acknowledging at the same time their resemblance to certain species of the Hirudinida or leech family. The Planaria have affinities with both these families, and lead from one to the other. Let us suppose we have under examination the largest of the British fresh-water Planaria, viz: P. lactea; this species varies a little in colour, which is either cream, roseate, or quite white; it is from six to ten lines in length, and about two lines in breadth; we first notice the delicate arborescent form of the digestive system; we place the creature on a glass slide and hold it up to the light, in its middle part we see a milk white spot which extends linearly towards the posterior extremity; by allowing the water gradually to evaporate, the animal shows signs of discomfort, and we observe a long cylindrical tube to be pushed out from a pore slightly posterior to the middle of the body: this pore is the mouth, and the tube is the proboscis, a formidable instrument of attack in these creatures; we notice two black oculiform spots, parallel, and placed on the anterior part of the back; a little below the oral aperture we see, but very indistinctly in P. lactea, another pore which belongs to the generative system; we find the body to be slimy, very soft, and readily breaking up if not handled with great care. Let us take another specimen of the same species, and with the aid of a camel's hair pencil, place it gently in a vessel of water, and observe its locomotive powers; we see it gliding in an even and regular manner, like a limax, or slug; if we touch it, the animal twists itself in various folds, or it fixes its head portion to the vessel, and, by contracting, brings the other parts of the body along, then the posterior part is attached, and the head portion elongates and advances. In the species Polycelis nigra, P. brunnea, Planaria torva, we observe the gliding locomotion to be frequently exercised on the surface of the water, the ventral side of the animals being uppermost; none of the true fresh-water Planaria can be said to swim; but an allied marine species, Leptoplana tremellaris, progresses by flapping its sides as a Ray its fins.* When we consider how varied and energetic are the movements of the *Dugès " Annal. des Sciences, Nat." xv. 151.

Planarian worms, for they can contract and elongate their bodies, fold themselves together in various forms, and unfold themselves, we naturally expect to find the presence of muscular fibres; how can such movements be explained except by the admission of the existence of a muscular system? And yet there are some animals of low organization, such as the small species of the Trematoda, which are endowed with active contractility, in whose bodies, notwithstanding, no muscular fibres have been detected. With respect to the Planaria many observers, as de Blainville, Dugès and others, entirely deny the existence of a muscular system, except in the proboscis, and genital organs; M. Quatrefages, on the other hand, describes a sub-cutaneous plane of muscular fibre, as being recognisable in some species, and Professor Owen remarks that in the Planaria, in which as in the Tania, according to his observations, the muscular system is indicated only by the striæ on the superfices of the apparently homogeneous parenchyma, the phenomena of muscularity are strikingly displayed in the varied and energetic actions of the living animal. My own investigations have satisfied me of the existence of a sub-cutaneous plane of loose muscular fibre in the fresh-water genera, Planaria and Polycelis. A nervous system in some species has been recognised by de Quatrefages, who describes it as "consisting of two ganglions, more or less intimately united, which are situated in the mesial line, near the anterior part of the body. This double ganglion, which may be called the brain, and which is sometimes visible to the naked eye, is lodged in a special lacuna or cavity, recognisable from its transparent outline, and is seen to give off nervous filaments in various directions to different parts of the body."+ In vain have I laboured in search of the faintest indications of a nervous system in the species I have examined. The relation of the Planaria to the Flukes, as already noticed, might lead us to expect the existence of a rudimentary nervous system in them as in those Entozoa, nevertheless, I think that we must still consider its presence in the fresh-water species as a subject requiring verification. Professor Rolleston, who, at my request, kindly repeated his examination of many specimens of Planaria lactea, says, "With reference to the nervous system of this species, I have never been quite satisfied that it was a real existent thing. Leydig says he has failed to see it sometimes in the fresh-water Planaria; but that the analogy of the marine Planaria, where a nerve-system is undoubtedly present, has forced him to look for it, and that he believes that a couple of pear-shaped ganglia underlying the two eyes, and *Todd's "Cyl. of Anat." ii., p. 128. + Rymer Jones, "General Structure," p. 146.