Page:Popular Science Monthly Volume 76.djvu/138

134 is demanded by the logic of the law of evolution. But just what they feel and to what degree they think is largely unknown. In the solution of these fascinating problems enduring biological research will give us knowledge where metaphysical speculation has left us groping and fencing with a jargon of terms.

Among the general problems to be solved in marine stations none are more interesting than those concerning the countless millions of organisms, that float in the surface waters as the plankton. Professor Théel has investigated these matters in the neighborhood of Fiskebäckskil since 1874 and has published important conclusions as to the origin and fate of the plankton. While most of these organisms constitute the holoplankton, always swimming freely, yet many, especially in the breeding season, belong to the meroplankton, swimming as larvæ only part of the time and then going to the bottom to form the benthon population, or to become anchored for the rest of life like the corals. One mystery at Kristineberg is that while many chætopod worms live in the bottom ooze their swimming larvæ appear but rarely in the plankton. On the other hand some forms occur at times in such masses as to make the water thick. Here, as on other seashores, the phosphorescent protozoan Noctiluca miliaris has been cast up in windrows of glowing greenish blue living fire. This tiny creature, in common with many other organisms, emits light when touched or rolled about, or upon chemical or electrical stimulation. It is possible on a dark night to read by their phosphorescence, which after all is but a secretion of their photoplasm on fire.

In the bay near Kristineberg from 1890 to 1900, the irregular sea-urchin Echinocardium cordatum occurred in large numbers but in the summer of 1902, none of the adults were found and only the young of one centimeter, or less, in size. It is the view of Professor Théel that in such cases, during some unfavorable years, the currents of the sea bear the swimming larvæ away from the ancestral breeding ground where, during their metamorphosis, they may be eaten by hungry hunters, or else sink in the abysmal waters and perish. If they find favorable bottom they will there establish a new race while the old unreplenished parent stock dies out. Thus in 1902 new larvæ of Echinocardium came to Kristineberg bay and reestablished the colony in its former home.

So animals appear and flourish in a region only to die out, while others come in to take their places. The rise of the herring fishery in these waters within the last forty years has seen the decline and practical extermination of the oyster business. In view of the fact that the planktonic larvas, while free-swimming yet depend upon the sea-currents to place them upon the right bottom, it is no wonder, that many perish in the constant struggle for existence. It is only because of the