The Rotatoria are divided (1) into those in which the female always has, and those in which it has not an anal orifice to the intestine; (2) the former into (a) those that are permanently fixed, and (B) those that are free-living; (3) the former of these into (i.) separate, (ii.) colonial forms; the latter into those in which (i.) the body is rounded and apparently unsegmented, and (ii.) the body is saccular or flattened with apparent segments. Into the further details of this somewhat artificial classification we have not the space to follow the author. After reviewing the opinions of previous writers as to the systematic position of the Rotatoria, Eckstein points out that their direct alliance with the Annelida is opposed by the early appearance of segmentation in those forms; the view of Korschelt and Metschnikoff that the Rotatoria are allied to the Turbellaria by Dinophilus is affected by Graff's belief that that genus is a true Rotifer. The author would associate with the Rotifera the Gastrotricha, but, in truth, their systematic place is even more indefinite than that of the Rotifera themselves. Rotifer within an Acanthocystis.*-Dr. A. C. Stokes' account of an observation of a rotifer living within the rhizopod Acanthocystis chatophora is not perhaps written with any severity of scientific style, but it is evident that any abstract we could give of it would fail to convey a correct idea of the original. It is also the first instance of which we are aware, of astronomical time being applied to microscopical observations. "Recently one of these spinous creatures [Acanthocystis] appeared under my Microscope. It seemed to be alive and well, but within it near the armoured surface, was a semi-transparent moving something that was too active to have a right there. As the motions of this foreign body became more impulsive, it turned completely over and showed itself to be one of the rotifers. In size it equalled not more than one-third the Acanthocystis' diameter, but dwarfish stature was amply compensated by nimbleness. With a leap, prodigious for so small a creature, the rotifer dashed against the wall and hurled the rhizopod down the field, while the silicious spines snapped and flew. If the scene was exciting to the spectator, what must it have been to the Acanthocystis, with that jumping Jonah leaping among its vitals? It was no joke to either party. A struggle for life was going on under my very eyes. The rhizopod, with every particle of its jelly-mass surrounding the rotifer possessing digestive power, seemed calm, perhaps with the calmness of despair, but the rotifer-oh how she plunged! Not a moment did she rest, not a muscle did she leave unused, not a manoeuvre untried. The situation appeared a bad one for that rotifer, since she bade fair to be digested. She stretched herself and forced out the spinous armour until it seemed on the point of rupture; the Acanthocystis simply flattened the opposite side and waited, digesting. The rotifer leaped, she turned, she pushed with her two sharp toes against the wall; the The Microscope, iv. (1884) pp. 33-5. rhizopod rolled over the field, the spines were loosened and fell off, yet that rotifer remained in the corner where she first appeared, pressed down by the Acanthocystis' body-mass, although her efforts were continually nothing less than frantic. For six hours the struggle lasted; from 14 to 20 o'clock the microscopic creatures were under uninterrupted observation. Finally, after a short rest on the rotifer's part, there occurred one of the most amusing exhibitions of intelligence in these lowly organisms that I have ever seen. It was indeed a most masterly piece of strategy. The rotifer began to eat! Protoplasmic jelly, chlorophyll-corpuscles, half-digested food-particles, everything the Acanthocystis contained streamed down into the rotifer's transparent stomach. With short intervals, which she improved by butting against the wall, she ate until she arrived at the central nucleus, when, apparently perceiving that her object was accomplished, she stopped, and then-it really did seem as if she was celebrating her victory-then she laid an egg! The rhizopod once dead and half empty, the brave rotifer selected the spot at which she intended to leave, and left. It is a curious fact that, having chosen the place for exit, she continued to beat against that point only, until the basal plates were forced aside, and she was free. Circling once or twice around the dead Acanthocystis she darted from the field, followed by applause, and a few remarks of approval from the spectator. By 24 o'clock the ovum that had been extruded in my presence as well as in prison, which I had seen rolling down the half-empty Acanthocystis' sac, had accomplished a part of its internal changes, but an awkward movement displaced the cover-glass, and ruined all. Did that unhappy rhizopod in an absent-minded moment take in an egg, and did that egg eventually take in the rhizopod? Was the development of the egg so far advanced that the rotifer was hatched before it could be digested?" Cœlenterata. New Alcyonarians, Gorgonids, and Pennatulids of the Norwegian Seas.* -J. Koren and D. C. Danielssen have published another of their beautifully illustrated works on the fauna of the Northern Seas; they describe a new genus Duva, in which they place three new species, and the Gorgonia florida of J. Rathke, which is not the same form as the Gersemia florida of Marenzeller. The other new genus is Göndul, for which it is necessary to establish a new family of Pennatulids-Gönduleœ-characterized as having the rachis fixed, with developed bilateral pinnules, and furnished with long calcareous spicules. The stalk in Göndul has a canal in its centre, which is divided by four valves into as many longitudinal canals. The genus Cladiscus is removed from the family Protocaulidæ, where it was placed by Kölliker, to the Protoptolidæ, in consequence of the presence of well-developed "cells." A number of new species are * 4to, Bergen, 1883, xvi. and 38 pp. (13 pls.). described, but, unfortunately, only the diagnoses are given in English, the full details being described in Norwegian. There is, however, a brief description of the plates in English. Origin of Coral Reefs.*-Prof. A. Geikie sums up a considerable amount of evidence which has accumulated since Charles Darwin's theory on this subject was put forth, tending to show that the theory (essentially that of growth of coral in connection with subsidence of the sea bottom) is by no means universally applicable. Semper and Rein supposed that in some cases raised masses of sand or deep-water corals are formed which afford resting places for surface-growing corals; the form of the islands, Semper held, is caused by the death of the inner parts of the colonies of corals, and by the action of the tides. Mr. J. Murray, from observations made on the Challenger,' considers that volcanic cones, such as form most oceanic islands, tend to be reduced to submerged banks by the action of the waves; also that the raising of the sea bottom to such a height as to favour the growth of corals, is due to the unusually rapid accumulation near the shore of calcareous débris derived from dead pelagic organisms. These are so abundant as probably to represent upwards of 16 tons of carbonate of lime in suspension in the uppermost 100 fathoms of every square mile of the ocean. In the deepest water these appear to be dissolved before reaching the bottom, but they accumulate on shallow bottoms, and thus furnish foothold for sponges, various Cœlenterates, &c., which in return die and bring up the bottom to the level of reef coral growth. This, taking place on a submerged bank, would produce the atoll form of island, which would tend to widen by death inside, and by the consequent solution of the dead coral by the carbonic acid of the sea-water. Special cases, such as elongate chains of atolls, e. g. the Maldives, or submerged banks, as the Chagos, fall in with the theory. Barrier reefs are similarly explained as due primarily to growth upon accumulations of débris around land. Porpitida and Velellida.t-We have here a notice of the work of A. Agassiz on these little known Hydrozoa. Velella mutica, of the coast of Florida, is much larger than the Mediterranean V. spirans, and not unfrequently reaches 4 in. in length. It is exceedingly common in Key West Harbour, which it visits in large schools. Feeding is chiefly effected by the large central polypite of the system, and this, together with the smaller polypites, is connected at its base with the general vascular system, through which, as in the polypites, the fluid is rapidly propelled by the lining cilia. At the base of the polypite are the medusoid buds, and these, it is interesting to note, early become provided with the yellow cells which are characteristic of the free Medusa. The young present a striking resemblance to certain Tubularian Medusa, being provided with a row of lasso-cells which extend from the base of the tentacles to the abactinal pole. The Floridan species of Porpita (P. linneana) is, similarly, larger than the Mediterranean P. mediterranea; unlike Velella it has a * Nature, xxix. (1883) pp. 107–10. + Mem. Mus. Comp. Zool., 1883. Sec Nature, xxix. (1884) pp. 262-3. considerable power of control over its own movements, and is by no means so much at the mercy of the winds or waves. If upset in the water it returns to its original position by bringing its tentacles together over the disk, and throwing up the free edge of the mantle in a given direction, then expanding the tentacles of one side far over in the opposite direction beyond the central part of the disk; thus, it readily changes the centre of gravity and tilts the overturned disk back again. Medusæ are to be found at all stages of development. Prof. Agassiz suggests that Porpita is allied to the Hydrocorallina, and he bases this suggestion on the possession of the so-called white plate, the peculiar structure of which reminds him of the corallum of Sporadopora, Allopora, and Millepora; there are large pits, and the whole mass is spongy from being riddled with passages and openings; but there are not, of course, the regular horizontal floors which are seen in Millepora. The value of the paper is greatly increased by the twelve plates, two of which give coloured full-sized representations of the two species described. Porifera. Physiology of Gemmules of Spongillida.*-To this subject, which is now exciting considerable interest, Dr. W. Marshall contributes some arguments and observations which should be compared with those given by Dr. Vejdovsky (see below). The wall of the gemmules of Spongilla nitens (as of S. carteri) consists of a system of closed spaces or cells. In S. nitens they form six-sided columns with their long axes tangential to the central mass; they diminish in size towards the interior of the gemmule; the outer cells are hollow and in the dry state filled with air, the innermost are solid. These cells are not histological cells, but of cuticular character; their walls are strongly refractive, and resist combustion stubbornly; fluoric acid destroys their refractive power and brittleness, so that it appears not improbable that they contain a large proportion of silica; the inner layer of spined spicules is attached to this cellular layer with more firmness than to the subjacent horny layer. S. nitens has an air-space, formed by the chitinous layer, as in S. carteri, which enables the dry gemmules to float for from 8 to 10 days in water. The elaborate envelopes which cover the abundant starch which accompanies the germinal matter provide in the most satisfactory manner for the protection and welfare of this material. Various arguments are advanced in favour of the aerostatic character of the cellular coat of the gemmule, viz. the smallness and, owing to the great relative development of this layer, the lightness of this body in S. nitens. In the districts where the sponge occurs it must often be left dry by evaporation and the gemmules subsequently set free may be carried long distances by the wind, and eventually germinate if they meet with fresh water again. Thus, of Ehrenberg's figures of organisms found in trade-wind dust, about 24 per cent. refer to sponges, and of these fragments about 16 *Zool. Auzeig., vi. (1883) pp. 630-1, 618-52. per cent. (4 per cent. of all the organic remains) are whole or fragmentary amphidisks of Spongillida; the absence of entire gemmules is explained by the distance which Ehrenberg's dust had travelled, viz. to Europe from (probably) North-west Africa. By experimenting directly on gemmules of Spongilla lacustris and nitens, by drying them for 8 days, piling 50 of each species together into one heap on a smooth plate, and blowing at them with a bellows, it was found as the result of this operation, repeated six times, that the gemmules of S. nitens were scattered to a greater distance than those of lacustris, viz. 75 per cent. beyond a radius of 5 centimetres, as against the 64 per cent. of those of the other species which stayed within this radius. The gemmule of the South American species Parmula Brownii has a very compact spicular shell, the spicules show a tendency to radiate from points at which the capsule is in contact with the true envelope of the gemmule: the latter envelope is covered with conical eminences which fit loosely against the outer capsule while dry, but come closely against it after soaking for some time in warm water-probably showing that it is a special arrangement to allow of the expansion of the germ, the outer capsule having no opening. The shield-like spicules overlap and cover all the surface of the inner envelope except the eminences just described. The outer capsule is usually firmly united to the surrounding skeleton. The sponge is known to affect, as its rooting places, stones which are alternately wetted and left dry. Thus, the close connection of the skeleton with the capsule secures it from being detached when dried, and the overlapping arrangement of the shield-like spicules prevents excessive collapse of the tender underlying envelope. The heaviness of the gemmules of Spongilla lacustris, and their projecting spicules (like the hooks of Polyzoan statoblasts) tend to anchor them and prevent undue rapidity of transportation by currents. The gemmules of the allies of S. fluviatilis are heavier than those of lacustris and allies, and hence are less mobile and better adapted to rapid streams. The three layers of amphidisks in the gemmule of Meyenia mirabilis Retzer (a recently described species) are perhaps an adaptation to very rapid waters. Marshall thinks it not inconceivable that external circumstances (e. g. long sojourn in still water) might transmute Spongilla (Euspongilla) into Meyenic, and vice versa; of the present occurrence of these changes perhaps Euspongilla jordanensis var. druliæformis Vejdovsky affords an example in the transitional characters of its gemmule spicules. European Fresh-water Sponges.*-Dr. F. Vejdovsky supplements his former study of this subject † by some additional observations: firstly he establishes the new species Ephydatia amphizona for the form previously described by him as Eph. Mülleri forma B., reserving *Abh. Böhm. Gesell. Wiss., 1883. See Ann. and Mag. Nat. Hist., xiii. (1884) pp. 96-8 (1 pl.). + See this Journal, iii. (1883) p. 858. |