74 8 THE POPULAR SCIENCE MONTHLY. 



oxygen that is held in the water. The stream also whirls minute bod- 

 ies, microscopic animals and plants, to the mouth, which swallows 

 them. Our terebratula has no other means of getting food. As the 

 oyster and the rotifer are fed by the streams and whirlpools produced 

 by the cilia?, so also is the terebratula. When the shell is closed, only 

 the exchange of gases takes place ; but when it is opened, or when 

 the animal is gaping, it is eating, for these larger bodies are drawn in 

 through the whirling. That this really takes place is shown by the 

 contents of the stomach, in which we may observe undigested remains, 

 the silicious shells of plants, diatoms, or Eadiolarice, and the needles 

 of fungoids. The organic substance is digested and dissolved in the 

 stomach, while the undigested remains are expelled through the 

 mouth. Sea-water, especially near the ground, to which the terebrat- 

 ula3 are attached, swarms with shell-protected and naked matter of 

 this kind. The terebratula is, moreover, in the happy situation of hav- 

 ing nothing to do but spit out the shells, for the meat itself flies into 

 its mouth. 



Every fixed animal produces moving young. Were this not the 

 case, the animals could not be distributed into spaces beyond their 

 immediate abode. Very curious young are produced from the eggs 

 of our arm-foots, which do not at first resemble their parents at all ; 

 larvae that swim around in freedom, having eyes, and armed with bris- 

 tles. They so much resemble the larva of some of the ringed worms, 

 that one would be apt to suppose at first sight that they were of that 

 kind. But after a time of wandering they settle themselves down, 

 and there then takes place, with the formation of the shell, a retro- 

 grade metamorphosis, by which the animal is gradually brought back 

 to its definite form. It is therefore easy to conceive that our arm-foot 

 leads a very safe life, and that, protected as much as possible against 

 enemies and other dangers, it can spin out its existence as long as the 

 sea does not dry up. Of course, in their younger days, the wandering 

 larvae may be swallowed up in numbers by other animals, but when 

 the young brachiopod is once fixed, the shell, the mantle-edge with 

 its bristles, and the ciliary apparatus protect it so well, that not even 

 parasites can attack it. Although fungoids, other animals, and occa- 

 sionally fellow-beings of its own race may establish themselves on the 

 outside of its shell, and load it to a certain extent, but otherwise do it 

 no harm, no parasite has ever been seen within. The little wart that 

 appears on the glass terebratula in the picture is one of their young. 

 There have always been fishes which, after a fashion, eat corals and 

 crush them with their hard teeth, to digest the polyps which the corals 

 contain, and expel the lime-substance ; but I hardly think they would 

 take in, the arm-foots, whose bodily substance is so stringy and yields 

 so little nourishment. In the deep sea, also, the animals are thoroughly 

 protected against the sudden changes of temperature which animals 

 living in shallow waters and near the shores have to encounter. 



