Page:Popular Science Monthly Volume 35.djvu/683

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ed are seen swimming backward and forward. When looked at through a microscope we see young jelly-fishes, the young of barnacles, crabs, and shrimps, besides the adult microscopic species, which are very abundant. The toothless whale finds in these his only food. Rushing through the water, with mouth wide open, by means of his whalebone strainers the minute forms are separated from the water. Swallowing those obtained after a short period of straining, he repeats the operation. The abundance of this kind of life can be judged from the fact that nearly all kinds of whales exist exclusively upon these animals, most of them so small that they are not noticed on the surface. Prominent among the animals obtained from the surface towings is Sapharina, a small crustacean which is remarkably iridescent, flashing in the sun-light with metallic colors. It darts swiftly about, now green, now blue, and very conspicuous on account of its ever-changing hues. Another similar form is red. At all times, and in nearly all places, both in the Gulf Stream and in the warmer waters outside, there is an interesting transparent animal called Salpa. At PSM V35 D683 Doliolum an ascidian allied to the salpa.jpgFig. 9.—Doliolum (an Ascidian allied to the Salpa), first glance it would appear to be structureless, but, if carefully studied, a mouth, a stomach, and other organs will be found, which place it among the higher invertebrate animals. They swim around in large schools, but on account of their great transparency are scarcely visible. Whether or not they serve as food for other animals I do not know, but it seems that a meal made of them would be rather unsatisfactory on account of the great quantity of salt water that enters into their construction. They often have a curious blue parasite inside the body walls, and this is about the only visible sign of structure. Very few. animals are free from parasites, and in the fishes they are numerous, burrowing into the gills, in the roof of the mouth, and all over the external portions of the body. On sharks we sometimes find them four inches long, an inch of which extends into the flesh. There is one called Penella, which is very long, and has a hairy tuft on the outer end. In most cases this parasite has attached to the external stem a species of barnacle, which itself has small parasites. Parasitic tendencies degenerate an animal, so that many of the once essential organs become useless and are lost. We see this well illustrated in Penella, which is an ally to the shrimp, but has so changed, by losing its feet and other organs, as to bear but little resemblance to these higher crustaceans. Degeneration is still