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Genus Mastigocerca, Ehrenberg.
Generic characteristics : Body fusiform, or irregularly thick. Toe a single style, with accessory stylets at its base. Lorica often furnished with a thin dorsal ridge.
VI. Mastigocerca flectocaudatus, sp. nov. Plate VIII., fig. vi.
Specific characters: Body compressed, flat ventrally, arched dorsally, and bent down anteriorly. There is no dorsal ridge. There is a long toe, nearly as long as the body, and a single long substyle, two-thirds as long as the toe. Cervical eye.
No colour except what is caused by highly refractive brown cells in the walls of the stomach. This Rotifer almost invariably swims on its side, and so a side view is by far the most familiar. It is more than three times as long as it is high, and the outline of the body is made up of long curves. The height is probably greater than the breadth, since the usual position in swimming under the cover-glass is on the side. This fact, however, may be explained by the bend in the foot, to be described now. The foot proper is very short and indistinct, but bears a very long style and a shorter sub-style, which are bent downwards, and which are incapable of being straightened; moreover, they are set in the foot with a downward inclination, and so always have a general direction at about right angles to the body. This fact would account for the Rotifer not swimming on its ventral surface when under the pressure of the glass. The style is more than two-thirds as long as the body and head of the Rotifer, while the substyle is two-thirds as long as the main style. The foot is often bent so that the tip of the style touches the anterior
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part of the body. The head is not distinctly marked off from the rest of the body; it is bent down-wards, so that the corona is inclined at an angle of 45° to the plane of the rest of the body. The lorica is very poorly developed, and seems to be more or less pliable. It becomes very soft indeed in the posterior region of the body, but is a little stronger in front, where it forms a small spine on each side. This spine has a much smaller spine just below it. The trophi are of the abnormal forcipate type, and show the want of symmetry characteristic of the family. The left malleus is very long, but the right one is greatly reduced, both in thickness and length. The stomach is surrounded by a number of brown highly refractive bodies, which seem like glands. No brain was observed. The eye is small and round; it is situated above the anterior part of the mastax, and is well back within the body, being very far behind the anterior border of the lorica, which may be said to mark the head from the body. The ovary is small, and is situated posterior to and below the stomach.
This Rotifer's movements are active and restless. It almost always swims on its side—at least, when on a glass slide. Its jaws worked only very rarely. Occasionally it anchored by the tip of its style, held this rigid, and waved itself about from the joint at its foot.
Hab. The pool.
Very common in autumn.
VII. Mastigocerca rectocaudatus, sp. nov. Plate IX., figs, vii., vii.a.
Specific characters : Body a long oval, no ridge on lorica. Toe exactly straight, and slightly longer than the body and head. Substyles 4, minute.
No colour except the small red eye. Seen from the side this is a slightly hump-backed Rotifer, with the highest point in the middle; it is also broadest in the middle, and tapers towards the extremities, more so towards the posterior one of course. A symmetrical and rather graceful Rotifer. The foot is short and rather indistinct, but it has an immensely long style, quite as, long as the rest of the body. This, as in M. flectocaudatus, is always carried at an angle to the general direction of the body. It is surrounded by three or four minute substyles. The head projects forwards and downwards from the body. The cilia must be very small, for I never saw them. The lorica is soft and flexible, though more developed than in M. flectocaudatus. There is a small median dorsal cleft, and the hinder border over the foot is concave. The mastax is of the asymmetrical type. The length and strength of the right malleus are very much
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reduced, and the right side of the split ramus is also reduced in size. The stomach is plainly marked off from the rest of the alimentary canal, is of large size, and situated rather on the right side of the body. The intestine passes backwards and opens into the cloaca, just anterior to the joint between the foot and the body. No foot-glands were observed, though doubtless they occur, since the Rotifer frequently anchors itself by the extremity of its style. The small red eye-spot is situated well within the anterior border of the lorica. When the head is retracted the trophi move back into the middle of the body, and the eye mores back too, as if it were fastened to the muscles surrounding the mastax. The eye is situated deep down in the body; it is concave on its anterior face, as if it were the posterior border of a transparent globule, which is probably a refractive lens. I was able to make out no more of the internal organs, owing to the unusual opacity of this Rotifer.
The movements of M. rectocaudatus are swift and erratic. It seems at times to go into a dormant condition, and does not move for hours. It usually swims on its side, but sometimes its back is presented to the observer. The head is then almost hidden, owing to its downward flexure. The head is often retracted wholly within the body; then the median anterior cleft in the lorica is very clearly seen, and the mastax moves back into the middle of the body. When the Rotifer anchors by its style it waves itself about at the foot-joint, just as M. flectocamdatus does.
Hab. The small pool, and another one near it.