Page:Popular Science Monthly Volume 30.djvu/656

634 hauled in, turned inside out, and rinsed by immersion and agitation in a bucket of water kept in the bottom of the boat. In this way everything entangled in the meshes of the net is transferred to the pail. The net is again put out and the operation repeated.

Skimming may be performed at any hour of the day; but in the daytime the forms collected will differ considerably from those captured at night, and, besides, will not be nearly so numerous. The best place for skimming is a spot where two tidal currents meet, forming a line of scum upon the surface; the best time is in the evening, when the surface of the water is calm and smooth. Then the wealth of forms and individuals is almost incredible, and no one who has never seen the operation can have the slightest conception of the results. Each time the net is hauled from the water it shines like molten gold from the phosphorescence of the myriads of animals by which it is covered. On closer examination it is seen that spots of other colors exist among the prevailing yellow light: bright red, blue, bluish-green, emerald-green, and white occur, and after some experience one learns to recognize the presence of a few species by the color of the light.

Only two or three hauls of the skimming-net are necessary to insure an abundance of material for study, and at no time need the student spend more than half an hour in this work, while frequently ten or fifteen minutes are ample. The laboratory is now sought, and the contents of the bucket in which the net was rinsed are poured into shallow glass dishes placed between the student and a lamp. Then, and not till then, does one begin to realize the enormous amount of life in the sea. In half an hour's skimming not a thousand gallons of water will pass through the net, and yet but a single glance at the dishes convinces one that millions—yes, millions—of individuals have been captured! The water is roily with minute animals and embryos, whirling, dancing, and jerking about in the strangest manner.

On different nights the relative proportion of forms will vary. Tonight not a single specimen may be taken of a species which last night was very abundant; but at all times a large proportion of the captures will be found to be copepod crustaceans—small forms not over a quarter of an inch in length, which swim about in a jerky manner by means of violent strokes of their long antenna?. To enumerate all the forms which might be taken by skimming would prove a difficult task, but some of the more prominent forms are readily recognized by the peculiarities of their motions. The Crustacea move by jerks, the embryo worms and mollusks, on the other hand, whirl away in a mazy waltz; while the jelly-fish swim lazily away by the languid contractions of their umbrellas.

While a general view of the results of surface-skimming is interesting and instructive, our student has other work before him. He is to take one species of embryo and follow it through its transformations. Soon after the dishes are placed before the light, most of the forms will