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But finally a firm backbone and skull were attained. The appendages. Of these we can say but little. The fish has oar-like fins, attached to the body by a joint, but themselves unjointed. By the amphibia legs, with the same regions as our own and with five toes, have already appeared.
Another member of this group is Daphnia, although the appropriateness of this name yet remains to be discovered; Daphnia being a chunky-bodied little being, with a double-branched pair of oar-like appendages, with which he darts swiftly through the water. Although covered with a hard crust like a crab, this is so transparent that we can see right through his body.
In some animals, the weight of the body is sustained by immersion in a fluid as dense as itself. It is then carried about with very little expenditure of effort, either by the waving action of vibratile cilia scattered over its external surface, or by the oar-like movement of certain portions of its frame especially adapted to the purpose.
See that musk-rat, how boldly he plunges into the stream, and, with his oar-like tail, stems the current till he gains in safety the sedges on the other side. What gurgling sound is that? it attracts the practised ear of the old hunter. What is that object which floats so steadily down the middle of the stream, and leaves so bright a line in its wake? it is a noble stag.
Then we shall often come across a queer creature with two oar-like feelers near the head and a double tail tipped with long hairs, while in the centre of the head is a large, shining eye, Cyclops he is rightly called.
Not less wonderful were the boatmen, swimming on their backs, pulling themselves along with a pair of oar-like legs. Great was the delight of brothers David and Daniel and myself when father gave us a few pine boards for a boat, and it was a memorable day when we got that boat built and launched into the lake.
The quick jerk of the dabchick's oar-like wings caused much wonder to Lutra, when, walking on the river-bed, she looked up towards the moonlit sky, and saw the little grebe dive like a dark phantom into the deep hole beneath the rocky ledges of Penpwll. Once the otter-cub, acting under an irresistible impulse, swam towards the bird and tried to seize him.
When the Ascidia-larva has attained this stage of development it begins to move about in the ovolemma. This causes the membrane to burst. The larva emerges from it, and swims about in the sea by means of its oar-like tail. These free-swimming larvae of the Ascidia have been known for a long time. They were first observed by Darwin during his voyage round the world in 1833.
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