Science in Germany

Abstract

(From a German Correspondent.) IN the twenty-fifth volume of the “Zeitschrift fur Wissen-schaftliche Zoologie,” just completed, Ehlers has given some interesting conclusions with respect to the distribution of the Chætopoda which were collected during the Porcupine expedition, by Messrs. Carpenter, Wyville Thomson, and Gwyn Jeffreys (“Beiträge zur Kentniss der vertical Verbreitung der Borstenwürmer im Meere”). He finds, in the first place, that of all Chætopoda occurring on the European coasts of the North Atlantic Ocean, only two families show representatives in the greater seadepths at more than 300 fathoms, and he thinks, therefore, it is not certain that any forms belong exclusively to the deep sea. Further, the conditions of temperature of the water, as they determine the horizontal distribution of Chætopoda, seem also to be of influence with regard to their vertical distribution, seeing the deeper layers of water are also the colder. Accordingly the forms that live in the cold deep sea of that zone of the Atlantic Ocean correspond with those of the coast fauna of the Arctic regions; and Ehlers thinks that they might even have a direct connection through currents which descend from the Arctic regions to the depths of warmer marine zones. It is also conceivable that the deep-sea forms, at a time when those regions of the Atlantic were warmer than they are now, were frequenters of the coast, and in proportion as the Gulf Stream heated the upper layers, they retired into the depths. For the most part they remain inferior to their Arctic congeners, perhaps because the conditions of existence in the depths are less favourable, and partly, doubtless, on account of the lack of plant life, and also the small amount of animal nutriment for the worms, there provided. Though in the greater sea depths the light is quite excluded, yet in the Chaetopoda found there (with some raje exceptions) we miss neither the colours nor the eyes, which are met with in coast regions. Ehlers believes that these colours and eyes are preserved in the lightless depths, in consequence of new animals ever migrating down from the brighter layers of water, and so preventing the disappearance of these body-parts. There is, however, in the same “Zeitschrift” which contains Ehlers' work, a paper by the physiologist Ranke, on the eyes of leeches (Hirudo medicinalis), which may explain that phenomenon in the deep-sea Chætopoda in a different way (“Beiträge zur Lehre von der Uebergangs-Sinnes-Organen”). Ranke, on the ground of his observations on living leeches, considers that their very simply constructed eyes have also sensations of touch and taste; and, further, that they are not eyes proper, which, on occasion, also serve other ends; they are, rather, neutral organs of sense, which can act in various directions, but in no particular one so Specially as sense organs more highly organised, and therefore limited to one specific energy. This appears partly from the fact that organs quite similar to these so-called eyes on the head of the leech occur also in the whole of the rest of its body, quite in the same way as the so-called side organs of fishes and amphibia, which probably afford sensations of touch. We might, then, regard the eyes of the deep-sea Chaetopoda as similar indifferent organs of sense, which, even where light fails, do not discontinue their functions. In an appendix to his memoir, Ehlers further describes how the tubeworms (Tubicola) construct their abodes. They use their feelers only for seizing and holding the building materials, then press these to the mouth or side of the abdomen, where they are coated with a cement secreted from numerous skin-glands in these parts of the body. So prepared, the piece has merely to be pressed on a firm bed, or the edge of a tube already formed, and there it adheres.