Art. XLVII.—Notes on Two Marine Gymnomyxa.
[Read before the Wellington Philosophical Society, 5th September, 1906]
Plates XXV and XXVI.
When tracing the development of a polychæte worm, in January of this year, I observed in the gelatinous matter in which the eggs of the worm were imbedded two Gymnomyxa—one a member of the Lobosa, the other nearer to the Labyrinthulidea than to any other class. I had these organisms under observation at the seaside during a fortnight; but I was not able in that time to fully trace the life-history of either. These notes must therefore be regarded as preliminary only.
Amœba agilis, n. sp. Plate XXV.
Endoplasm often not noticeably granular in appearance; pseudopodia varying, being sometimes blunt and rounded, at others tapering and flexible. Nucleus occasionally visible in unstained specimens; always easily seen in stained specimens. No contractile vacuole. Sometimes the animal is sluggish, but usually it moves quickly and, when well nourished, divides rapidly. When preparing for division the animal usually draws itself out into two masses, a more active mass drawing away, as it were, from a less active mass, the two remaining connected for a short time by an isthmus of non-granular matter, which finally gives way. In Plate XXV, figs. 1 to 27, are given outlines
of an Amœba preparing for division. It will be noted that the animal frequently draws itself out into two or more masses before finally dividing. In this case the preparatory stages occupied thirteen minutes. The new Amœba to the left in fig. 27 divided again in five minutes; that to the right in fifteen minutes.
Streaming of the endoplasm is very marked and often very rapid, with sudden reversal. Streaming and change of shape cease at the same moment. At this moment the animal has become somewhat pear-shaped, the broad end leading. Then comes reversal of streaming and of movement, either immediately or after a very short rest. It is usual for the animal to move four or five times its own length before reversal.
The food of the animal consists, so far as it is visible, mainly of small diatoms and other unicellular plants. When the animal comes near a diatom the latter approaches it at a very rapid pace, appearing to rush to it. I could observe no mechanism to account for this. Food-vacuoles could not be detected. Fæces were egested slowly or quickly; if quickly, at the end of a pseudopodium.
The average diameter of the animal is about 0·1 mm.
Myxoplasma rete, n. gen. et sp. Plate XXVI.
Body flattened, apparently because the protoplasm is too fluid to resist gravitation. This flattened body may surround two or more large spaces and several smaller ones. Delicate pseudopodia are emitted, and these often anastomose. The protoplasm streams along these pseudopodia, gathering itself into larger or smaller masses here and there. At first the pseudopodia do not contain granular endoplasm, but this streams in and often becomes separated from the main granular mass. A notable feature of the pseudopodia is that they often exhibit waving movements like those of the tentacles of many hydroids. This movement is generally slow. At times a mass of granular matter detached from the main granular portion and surrounded by non-granular matter may be observed to move rapidly along the margin of the body, as though its non-granular isthmus actually rushed along. This indicates great contractility, and at the same time great fluidity of the non-granular matter. Nuclei were not observed. In general appearance the body resembles closely an active plasmodium of a Mycetozoan; but whether it originates as such a plasmodium does I am unable certainly to say.
A slide that had been under observation for eight days was left unobserved for three days during my absence. When I
returned, the organism as I had observed it had disappeared. In its place were many active flagellulÆ, each with a well-marked nucleus and a large vacuole, non-contractile (Plate XXVI, fig. 5). The body of a flagellula is pear-shaped, with a long flagellum at the posterior end. Nothing like an eye-spot is visible. These flagellulÆ aggregated in places into small masses, losing their activity but not becoming fused. In connection with these quasi-plasmodia, or often not in connection with them, the flagellulÆ formed into long strings and loose networks. In this stage the resemblance to the fibres and spindle cells of Labyrinthula is unmistakable. I did not, however, observe any spindle cells that moved along the threads.
I am not, of course, sure that the plasmodium-like body that I have called Myxoplasma broke up into flagellulÆ. I am certain only that these appeared after Myxoplasma had disappeared, and that they united to form the Labyrinthula-like network. The network remained unaltered until I came to town, bringing it with me for permanent preparation.
The average long diameter of Myxoplasma is about 0·15 mm.