COPEPODA 753 



animals are not planted there. If the eggs of Copepoda were dis- 

 seminated to any extent with the dust by winds, conditions would 

 seem to be unusually favorable; for such ponds are found in dry 

 regions subject to heavy winds. "Dust storms" are very common, 

 and in them large quantities of dust are moved from one place to 

 another. Ducks, too, frequent these ponds in enormous numbers, 

 and are continually on the wing, moving from one place to another. 

 It would seem, then, that in the arid and semi-arid regions condi- 

 tions were as favorable as possible for these two methods of trans- 

 portation. Yet the fact remains that the ponds are frequently 

 almost entirely devoid of copepod life, and one must conclude 

 that these methods of dissemination are of minor importance. It 

 apparently follows from these facts that, when once a form has 

 reached a mountain lake, it may remain in undisturbed possession 

 for a long time, and thus, by the ordinary processes of evolution, 



. one may expect to find in mountain regions a great variety of 

 species. As a matter of fact, in parts of the country where water 

 communication is easy, as in the Mississippi Valley, there prevails 

 great uniformity in the species, while in the mountain regions of 

 the West one finds a greater variety of species. 



Tr^e ordinary means of collecting other forms of small water 

 animals and plants will serve for the Copepoda. The Birge net is 

 the most useful form of collecting apparatus. Inasmuch as Co- 

 pepoda are extremely common in open and clean waters, the wire- 



. netting cap of the Birge net (p. 68) can frequently be dispensed 

 with, and the apparatus thus simplified. A conical net of fine mus- 

 lin with the opening stiffened by a wire ring will serve admirably for 

 making collections. This can be dragged behind a boat, or, if 

 weighted, can be thrown from the shore to a distance of from thirty 

 to forty feet, care being taken, as it is drawn in, to collect as little 

 as possible of floating debris or of mud if it strikes the bottom near 

 shore. The material collected in the end of the net can, by in- 

 verting the net, be washed into a wide-mouthed bottle or tumbler 

 or tin fruit can, and then transferred to the homeopathic vials in 

 which it is stored. An easy way to make this transfer is to pour 

 the condensed material on little squares or circles of fine muslin, 

 two or three inches in diameter, and then place cloth and all in 

 the preservative fluid. 



