running down the gullet. Three kinds of eggs have been distinguished-common eggs, intended for immediate hatching; winter or resting eggs, designed for preservation probably till the next season, like the statoblasts of Plumatella and other Polyzoa; and male eggs. The winter or resting eggs are usually rough and large.

The known males are shortlived, and not provided with any digestive machinery. They seem to be simply locomotive organs of fecundation, whose services are occasionally required, the ordinary process of reproduction being carried on by the females alone, as is the case with those pests of the greenhouse and garden-the Aphides, or plant-lice. Such a method of propagation has more or less analogy to the multiplication of plants by buds or cuttings, instead of by germs fertilized by pollen and giving rise to true seeds.

The existence of eyes in rotifers has already been mentioned. They often exhibit the brilliance and tint of the ruby. and the single large eye of the Brachions may be specially noticed for its conspicuous beauty. In many rotifers the eyes vanish as the individual grows old, and it is often difficult to detect them. Dark ground illumination is frequently very useful for this purpose. The eye is probably of limited use, and may not form true pictures in the highest sorts of rotifers, though a refracting body or crystalline lens is said to be always present. There are many gradations in nature from eyes that seem only capable of making known the presence of light to those which form elaborate pictures on the retina, and by means of appropriate nerves supply definite information to the brain. Probably, the rotifer eye occupies one of the lower, though not the lowest position in the scale.

The calcar or spur of the common rotifer, often seen projecting like a pigtail, and similar organs on other species are probably feelers. They are tubular structures, fitted with a sort of moveable piston, terminating in a tuft of cilia. A sense of touch is probably diffused over the soft parts of the body, and the tentacles may be very sensitive to vibrations affecting the fluid in which the animal lives. It is also probable that the sense of taste exists in a rudimentary form, as it is very common to find rotifers rejecting particles which so far as size and consistency goes might be swallowed for food.

No perfectly satisfactory classification of rotifers has yet been proposed. Ehrenberg divided them into groups, founded upon his conception of the form of the rotary organs, but a modification or rather expansion of Dujardin's classification will be found more convenient for general use, and may stand as a provisional arrangement, pending a more thorough examination of the whole series. Dujardin calls rotifers Systolides,

from the Greek, ovσToλn, contraction, but as many other creatures exhibit contractibility in as remarkable a way, the name has not usually been considered appropriate, and has not come into general use. He divides his Systolides, which include water bears, into orders, as follows:-1. Those which are fixed by the posterior extremity of their body. 2. Those which have only one mode of locomotion by means of their vibratile cilia, or the swimmers. 3. Those which have two modes of locomotion, and which sometimes crawl like leeches, and at others swim like the preceding, or swimmers and crawlers. 4. Those which are destitute of vibratile cilia, but provided with claws and are veritable walkers-water-bears. It is desirable to exclude the water-bears from the group, and we shall then have fixed rotifers, swimming rotifers, and swimmers and crawlers. These divisions, though not founded upon any deep considerations of structure, indicate obvious and important facts. The fixed rotifers comprehend the Floscularians, which have long tufts of cilia, but no wheel-like organs, and the Melicertians, which have four lobes something like the petals of a flower, with cilia round their margins, exhibiting the rotatory appearances. The swimmers comprehend several genera, amongst which the Brachions, or pitcher rotifers, are conspicuous. Dujardin proposes two divisions of swimmers, one characterised by a general flexibility of the skin or integument, Furcularians, and the other, like Brachionus, Salpina, etc., having rigid carapaces or cuirasses. The swimmers and crawlers comprehend the Philodines, of which the common rotifer is the type. Many things might be said against accepting this scheme as a final arrangement of the group, but no harm can arise from its provisional use, provided that it is borne in mind that in addition to the modes of locomotion mentioned by Ehrenberg, jumping must be added as characteristic of several species, such as Polyarthra, Triarthra, and a few others. It would also be advisable to add to Dujardin's groups one of associated rotifers to include Conochilus and Lacinularia, which are inconveniently placed in his Melicertian family. There is an obvious and important difference between the permanent fixture, with confinement to one spot, of the Floscules, Melicerta, Ecistes, etc., and the free swimming of the associated groups of Conochilus. In both cases the creatures may anchor themselves by their tail-feet, but in one case there is permanence of abode and in the other a roving life.

The fixed rotifers differ very considerably from each other, and those which form simple tubes are easily distinguished from the Melicertæ, which are builders, constructing their abode of separate pellets moulded by an organ specially provided for the purpose, and placed in due order as a mason

arranges his stones or bricks. There are also obvious and important differences between the ciliary apparatus of the Floscules, which exhibit nothing like rotation, and those of the Ecistes, Limnias, or Melicerta, which do show that remarkable phenomenon, and in which it is subservient to the collection of food. In fact, Dujardin's order of fixed rotifers is so far unnatural, that it groups together families that must be separated in any system founded more upon structure and less upon obvious peculiarities of external appearance.

If we followed Dujardin's arrangement, we should begin by speaking of the Floscularians, which would not have been called "rotifers" or wheel-bearers at all, if they had been the first of the group to attract attention. The most conspicuous and decided wheel-bearer is the common rotifer, in which the rotatory organs serve the two purposes of locomotive engines and food collectors, and probably, also, act in assisting respiration by bringing fresh currents of water to the delicate tissues of the creature. When it pleases this rotifer to anchor herself by her tail-foot, her mode of life for the time resembles that of Ecistes or Limnias. Her ciliary currents cause a convergence of whirlpools, which bring all sorts of particles, living or dead within her reach, and she selects some for reception and others for rejection. This being ended, we find her swimming, or crawling, frequently routing about with the snout-like extremity she presents when her wheels are withdrawn, and apparently exerting discrimination in the selection of places to examine, and of food to take in. From this active, many-motioned animal, with powerful, whirlpool machinery at her command, let us pass to the beautiful Floscule, one of the most exquisite of rotifers, when properly exhibited by dark-ground illumination. If our illuminating apparatus is nicely managed we see an extremely delicate and transparent cylinder like a confectioner's glass, surrounding the creature, and forming her house. Slowly she rises, looking so uncouth that her appellation of "beautiful" seems inappropriate. But we must not be in a hurry to condemn her. Most gracefully she throws out her five lobes, and opens from each one a long tuft of cilia, gleaming and glancing in the light of our apparatus. If we keep quiet, the fans remain expanded and still. Each of the long hairs or cilia, of which it is composed, appears capable of transmitting delicate vibrations, and we frequently see a whole group of them twinkle in succession like the small steel vibrators of a musical-box when the instrument is playing. The animal can direct her head to any quarter, she can change at will the position of her richly-ciliated lobes, and thus cause the inward current which she maintains by less conspicuous cilia to bring to her mouth the particles she requires. Here the long cilia may be roughly

compared to the whiskers of the cat-they are collectors of a certain sort of information, not apparatus for catching food. If any object strikes rudely against the long hairs of the Floscule, she returns to her cell; and shaking the table will often induce her to do the same.

Let us now look at the Stephanoceros, the finest of all rotifers when seen in perfection, and a most voracious creature. Her cup-shaped body often seems nearly filled with green and golden monads and similar things she has swallowed. The dark ground illumination of the parabola or spot lens, in such cases, makes the creature look like a crystal goblet filled with emeralds and rubies. The five arms are something like the tentacles of the polyzoa, and they bear cilia at their edges. A little examination, however, shows us that the Stephanoceros arm cilia are not like those of a polyzoon in constant vibration, but more quiescent, like those of the Floscule. They are also much longer than those of the polyzoa-indeed, much longer than any of the drawings in ordinary books represent them, and much longer than any microscopist will have a chance of seeing them, who does not take great care of his illumination.

In Melicerta we come back to the wheel cilia, but the most noticeable peculiarity of this creature is her method of building her tube, which Mr. Gosse was the first to describe, though she was known to Leuwenhoek in 1703. Immediately below the angular chin of the Melicerta is a cup-like organ to which a ciliary current can bring particles to be "moulded with the help of some secretion into the pellets of which the little house is built up. Having formed her brick the Melicerta bends her head and deposits it in its place."

The tubes of the rotifers we have just considered are constructions, that of the Melicerta being an example of masonry, while those of Floscule and Stephanoceros are simpler, consisting of a gelatinous-looking exudation thrown off by the animal in the form of rings. In the case of Stephanoceros the successive portions are roughly joined, so that the divisions may be seen in the tubes of this species. In Limnias and Ecistes the tubes are gelatinous in aspect, and sticky on the outside, so as to cause the adhesion of extraneous particles. In the Floscule, the gelatinous-looking matter, whatever may be its chemical composition, is a very perfect transparent hydraulic cement, and the structure it forms is so thin and transparent as to be very easily overlooked.

If we pass from these tube-dwelling rotifers to the associated rotifers Conochilus and Lacinularia we do not find anything that can be fairly termed a tube. The rounded balls which they present to our notice, are composed of individuals more or less immersed in a gelatinous mass,

from which they escape when inconvenienced, or enfeebled by the pressure and confinement of a live box or compressorium. Probably the greater part of this gelatinous mass has no important action in keeping the colony or family in union-that object seems to be effected by their tail feet, which hold on to a central portion of the gelatinous matter. The different members of a Conochilus or Lacinularia group are probably, in every case, all one family; but I am not aware that any one has succeeded in watching the whole process of the formation of a group of Conochili, though it is not uncommon to find in Conochilus balls individuals varying in size and apparent age. When a Conochilus group is broken up, the individuals gyrate about as if utterly destitute of selfcontrol. They cannot walk or crawl, and their ciliary apparatus, unlike that of the free swimmers, is not adapted to execute the movements required by an independent being. When in a mass, the Conochili revolve, and roll through the water in various directions, and they must have some power of simultaneously modifying their ciliary action, or we should find them collected together on one side of a pond, or continually thumping against one side of a glass, which is not the

case.

The Conochilus is a free swimmer for the greater part of its existence, if not for the whole of it; but Lacinularia-which I know only from report-appears to be stationary, except when a young associated brood leave the parent mass, and swim away in search of a fresh location. Single Lacinularians are not, it is said, in the habit of making solitary journeys, though they resemble very closely Megalotrocha, which is described in Pritchard as "white and free when young, and yellowish and attached in radiating clusters when old."

We may now consider Dujardin's "free swimmers," the first section of which are provided with a sort of armour, carapace, or cuirass. He names them from this circumstance "cuirassiers." They comprehend Pterodina, Anourella (or tailless), Brachions (with tails), Lepadella, Euchlanis, Dinocharis, Salpina, Colurella, Ratula (or rat-tail), Polyarthra, and Triarthra, the former with several sword-like appendages, whence Mr. Gosse has given it the name of "sword-bearer," and the latter with their long styles used for a jumping method of locomotion. Asplanchna, of which we shall have to speak presently, belongs to this group. Dujardin describes this order as composed of "animals of variable form, some round and flattened, others ovoid, and either almost cylindrical or compressed, but their length never being more than double their breadth, covered with a membranous cuirass." [The term "membranous" is objectionable, firm or hard would be