Common objects of the microscope

by J. G. Wood

The form just referred to is a near relative of the Hydra, already described, and belongs to the same great family as the sea-anemones. One form, shown in Fig. [26], is the Hydra Tuba, long thought to be a distinct animal, but now known to be the young form of a jelly-fish, or Medusa. The Hydra Tuba throws off joints at intervals, each of which becomes a perfect jelly-fish. One of them is shown in Fig. [27]. Fig. [28] represents a very small and pretty Medusa, the Thaumantias. When this animal is touched or startled, each of the purple globules round the edge flashes into light, producing a most beautiful and singular appearance. Fig. [29] exhibits the so-called compound eye of another species of Medusa, though it would appear that these are really connected with the nervous system of the animal, and have to do with the pulsating contractions of the bell by which it is propelled through the water.

In my Common Objects of the Sea-Shore the Actíniæ, or Sea-Anemones, are treated of at some length. At Fig. [16] is shown part of a tentacle flinging out the poison-darts by which it secures its prey; and Fig. [17] is a more magnified view of one of these darts and its case.

Much more might be said under this head, but we must pass on to another group, which, whilst possessing a certain general resemblance to the hydroid zoophytes, differs utterly from them in internal organisation. We have already referred to the fresh-water polyzoa. The marine forms are vastly more numerous, and more easily found, since not only pieces of weed upon which they grow are to be found upon every beach, but whole masses of leaf-like colonies, forming what is known as horn-wrack, may be plentifully found. Instead of the tentacles armed with sting-cells, like the anemone’s, possessed by the Hydrozoa, the Polyzoa have arms clothed with active cilia, by which the food is swept into the mouth, passing on into the stomach, and then through the intestine to another opening.

Fig. [19] is a very curious zoophyte called Anguinaria, or snake-head, on account of its shape, the end of the polypidom resembling the head of the snake, and the tentacles looking like its tongue as they are thrust forward and rapidly withdrawn. Fig. [21] is the same creature on an enlarged scale, and just below is one of its tentacles still more magnified. Fig. [23] is the ladies’-slipper zoophyte (Eretea); and Fig. [24] is called the tobacco-pipe or shepherd’s-purse zoophyte (Notamia).

Fig. [22] is a portion of the Bugula, with one of the curious “birds’-head” processes. These appendages have the most absurd likeness to a bird’s head, the beak opening and shutting with a smart snap (so smart, indeed, that the ear instinctively tries to catch the sound), and the head nodding backward and forward just as if the bird were pecking up its food. On Plate XII. Fig. [2], is a pretty zoophyte called Gemellaria, on account of the double or twin-like form of the cells; and Fig. [5] represents the Antennularia, so called on account of its resemblance to the antennæ of an insect. Fig. [22] is an example of a pretty zoophyte found parasitic on many sea-weeds, and known by the name of Membranipora. Two more specimens of zoophytes may be seen on Plate [XI]. as they appear under polarised light. Fig. [17] is the Cellularia reptans; and Fig. [20] is the Bowerbankia, one form of which occurs in fresh water.

Among the worms we may refer to the beautiful little Spirorbis, whose tiny coiled spiral tube may be found attached to almost every sea-weed, and which, when placed in a trough of sea-water, protrudes its beautiful crown of plumes. In chalk or other soft rocks, again, the tubes of Spio, with its two long waving tentacles, may be found by hundreds. Then there are the centipede-like worms, which may be found under nearly every stone, and which belong to the great family of Nereids, provided with formidable jaws and stiff bristles of various forms. The Serpulæ are allied to the Spirorbis already mentioned. Parts of the so-called feet of one of these worms are shown in Fig. [36], where the spears or “pushing-poles” are seen gathered into bundles, as during life. One of them, on a larger scale, is shown in Fig. [32]. The gorgeous hairs of Aphrodite have already been alluded to.

In the sea the few species of Crustacea which fresh water offers to the observer in the shape of Cyclops and its allies become thousands, and their changes during development are numerous and puzzling. Who, for example, would suppose that the young stage of the Cyclops was indistinguishable in habits, and almost in form, from that of the barnacle which adheres to the rocks? Yet such is the case, and there are other metamorphoses even more startling. Fig. [25] is the larva of the common crab, once thought to be a separate species, and described as such under the name of Zoæa.

The Mollusca proper will not afford us many objects, except in the form of their lingual ribbon, which may be extracted from the mouth, gently heated in liquor potassæ, and mounted in balsam after well washing, when the rows of teeth form splendid objects by polarised light. The palate of a whelk is shown in Plate XI. Fig. [19].

Again, the gills of the mussel will afford a beautiful illustration of ciliary action. If a portion of the thin plates which lie along the edge of the shell be examined in a little of the liquor, the action may be splendidly seen, and watched for a long time (Fig. [39]).