Chapter 4 MARCH.

Paramecia-Effects of Sunlight-Pterodina patina-Curious tail-Use of a Compressorium-Internal structure of Pterodina-Metopidia-Trichodina pediculus-Cothurnia-Salpina-Its three-sided box-Protrusion of its gizzard mouth.

HE Paramecia, noticed in the last chapter, have increased and multiplied their kind without any fear lest the due adjustment between population and food should fail to be preserved. A small drop of the scum from the surface of the water in their bottle is an astounding sight. They move hither and thither in countless numbers, seldom jostling, although thick as herrings in a tub, and in many portions of the field the process of self-fissure, or multiplication by division, is going on without any symptoms of discomfort on the part of the parent creature. This is an interesting sight, but we will not linger over it, for the sun is shining, and there is enough warmth in the air to make it probable that the ponds will be more prolific than in the cold winter months. Sunshine is a great thing for the microscopic hunter; it brings swarms of creatures to the surface, and the Rotifers are especially fond of its genial beams. Even if we imitate it by a bright lamp, we shall attract crowds of live dancing specks to the illuminated side of a bottle, and may thus easily effect their capture by the dipping-tube.

Pterodina patina.

This year the March sunshine was not lost, for on the third of that month I obtained a bottleful of conferva from a pond about a mile from my house, and lying at the foot of the Highgate hills. Water-fleas were immediately discovered in abundance, together with some minute worms, and a ferocious-looking larva covered with scales; but what attracted most attention was a Rotifer, like a transparent animated soup-plate, from near the middle of which depended a tail, which swayed from side to side, as the creature swam along. The head exhibited two little red eyes; two tufts of cilia rowed the living disk through the water, and the gizzard worked with a rapid snapping motion, that left no doubt the ciliary whirlpools had brought home no slender stores of invisible food. Sometimes the end of the tail acted as a sucker, and fixed the animal tightly to the glass, when the wheels were protruded, and the body swayed to and fro. Then the sucker action ceased, and as the creature swam away, a tuft of cilia was thrust out from the extremity of the tail. A power of one hundred linear was sufficient to enable the general nature of this beautiful object to be observed, but to bring out the details, much greater amplification was required, and this would be useless if the little fidget could not be kept still.

450 Pterodina patina-gizzard.

The size of the creature, whose name we may as well mention was Pterodina patina, rendered this practicable, but required some care. The longest diameter of the body, which was not quite round, was about 1-120", so that it was visible to the naked eye, and as a good many were swimming together, one could be captured without much difficulty, and transferred with a very small drop of water to the live-box. Then the cover had to be put on so as to squeeze the animal just enough to keep it still without doing it any damage, or completely stopping its motions. This was a troublesome task, and often a little overpressure prevented its success.

Some observers always use in these cases an instrument called a compressorium, by which the amount of pressure is regulated by a lever or a fine screw; but whether the student possess one or not, he should learn to accomplish the same result by dexterously manipulating a well-made live-box. We will suppose the Pterodina successfully caged, and a power of about one hundred and fifty linear brought to bear upon her, for our specimen is of the "female persuasion." This will suffice to demonstrate the disposition and relation of the several parts, after which one of from four hundred to five hundred linear may be used with great advantage, though in this case the illumination must be carefully adjusted, and its intensity and obliquity frequently changed, until the best effect is obtained.

We find, on thus viewing the Pterodina, that it is a complex, highly organized creature, having its body protected by a carapace, like the shell of a tortoise, but as flexible as a sheet of white gelatine paper, which it resembles in appearance. Round the margin of this carapace are a number of little bosses or dots, which vary in different individuals. The cilia are not disposed, as at first appeared, in two separate and distinct disks, but are continuous, as in the annexed sketch. Down each side are two long muscular bands, distinctly striated, and when they contract, the ciliary apparatus is drawn in. As this contraction takes place, two apparently elastic bands, to which the ciliary lobes are attached, are bent downwards, till they look like the C springs behind a gentleman's carriage; and they regain their former position of slight curvature, when the cilia are again thrust out.

Pterodina patina-tail-foot.

The gizzard is three-lobed, and curiously grasped by forked expansions of the handles of the hammers. The tail, or tail-foot, can be withdrawn or thrust out at the will of the creature; and when in a good position for observation, a slight additional pressure will keep it so for examination. Delicate muscular longitudinal bands, forked towards the end of their course, supply the means of performing some of its motions, and one, or perhaps two, spiral threads extend through the upper half of its length, and either act as muscles, or as elastic springs for its extension. The intestines and other viscera are clearly exhibited, and a strong ciliary action conducts the food to the gizzard-mouth.

To return to the tail. One spiral fibre is easily discovered; but I have often, and at an interval of months, seen the appearance of two, and am in some doubt whether this was a deception, arising from the compression employed, or was a genuine indication.

A. Metopidia acuminata, as drawn by Mr. Gosse. B. Specimen as seen and described in text. c. Mouth or gizzard.

Where this Rotifer occurs I have usually found it plentiful, but unfortunately could obtain no constant supplies after I had determined to make a special study of the remarkable tail, which is much more complicated than I have described. The Pterodina lived for some time in captivity, and for a week or two I could obtain them from my glass tank. They were likewise to be found for some weeks in the same part of the pond, but not all over it, until one day not a single specimen could be discovered, notwithstanding a persevering search nor was I afterwards able to get any from that pond during the remainder of the year.

Trichodina pediculus.

Several other Rotifers, with and without carapaces, were among the same mass of conferv?, among them a Metopidia, with a firm shell, a forked jointed tail, and a projection in front which worked like a pickaxe among the decaying weed. There were likewise specimens of the long-necked animalcules (Trachelii), groups of Vorticella, some specimens of Volvox, and a small Trichodina pediculus, which, when magnified two hundred and sixty linear, was about the size of a sixpence and equally round. The edge was beautifully fringed with a circle of cilia; in an inner circle was a row of locomotive organs, and the centre exhibited vacuoles constantly opening and shutting. This creature, as before explained, is often found as a parasite upon the polyps. On one occasion a glimpse was caught of a Rotifer similar in shape to the common wheel animalcule, but with a yellow inside. Possibly it was the object so beautifully delineated by Mr. Gosse, in his "Tenby," and described as the "Yellow Philodine," but this must remain in doubt, as it managed to escape before it could be secured.

A. Cothurnia imberbis-('Micrograph. Dict.') B and C. The specimens described in text. The figures give the linear magnification.

By the 18th of the month the Vorticellids were much more plentiful, and their changes easily watched; many left their stalks while under the microscope, after which some rushed about like animated and demented hats, others twirled round like tee-to-tums, while others took a rest before commencing their wild career. But the common Vorticell? were not the only or the most interesting representations of their charming order, for upon some threads of conferva were descried several elegant crystal vases standing upon short foot-stalks, and containing little creatures that jumped up and down like "Jack in the box." These were so minute, that a power of four hundred and thirty linear was advantageously brought to bear upon them. When elongated their bodies were somewhat pear-shaped, but more slender, and variegated with vacuoles and particles of food. The mouths resembled those of Vorticell?, and put forth circles of vibrating cilia. They were easily alarmed, when the cilia were retracted, and down they sank to the bottom of their vases, quickly to rise again. In one bottle there were two living in friendly juxtaposition. This was not a case of matrimonial felicity, nor of Siamese twins, but of fission, or reproduction by division. The original inhabitant of the tube finding himself too fat, or impelled by causes we do not understand, quietly divided himself in two, and as the house was big enough, no enlargement was required. How many stout puffy gentlemen must envy this process; how convenient to have two thin lively specimens of humanity made out of one too obese for locomotion. Man is, however, sometimes the victim of his superior organization, and no process of "fission" can make the lusty lean.[9]

[9] Balbiani in his 'Recherches sur les Phénomènes Sexuels des Infusoires,' speaks of the Vorticellids as the only Infusoria dividing longitudinally. In other species such appearances arise from conjunction.

The bottles in which these creatures live, in happy ignorance that they are called by so crackjaw a name as Cothurnia imberbis, were described as Carapaces by Ehrenberg, but they bear no resemblance to the shell of a turtle or crab. They are thrown off by the animals who preserve no other connection with them than the attachment at the bottom.

The Micrographic Dictionary describes the family Ophrydina as corresponding to Vorticellina with a carapace. Stein places them with Vorticellids, &c., amongst his Peritricha, which are characterised by a spiral wreath of cilia round the mouth.

Towards the end of the month a great number of black pear-shaped bodies (Stentor niger), visible to the naked eye, were conspicuous in some water from the Kentish Town ponds. Upon examination they were found to be filled with granules that were red by reflected, and purple by transmitted light. Each one had a spiral wreath of cilia, with a mouth situated like those of the stentors, hereafter to be described, but none of them became stationary, and in a few days they all disappeared. Stein divides Ehrenberg's Stentor igneus from S. niger; the creature described seems to have agreed with Stein's igneus, which he describes as having blood-red lilac, cinnabar, or brown-red pigment particles, and as much smaller than his S. niger. In the same water were specimens of that singular Rotifer, the Salpina, about 1-150" long, and furnished with a lorica, or carapace, resembling a three-sided glass box, closed below, and slightly open along the back. At the top of this box were four, and at the bottom three, points or horns, and the creature had one eye and a forked tail. Keeping him company was another little Rotifer, named after its appearance, Monocerca rattus, the 'One-tailed Rat.' This little animal had green matter in its stomach, which was in constant commotion. I ought to have observed that the Salpina repeatedly thrust out its gizzard, and used it as an external mouth. In the annexed sketch the Salpina is seen in a position that displays the dorsal opening of the carapace. Its three-cornered shape is only shown by a side view.

Here we close a brief account of what March winds brought in their train. The next chapter will show the good fortune that attended April showers.

Salpina redunca.

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