[5] AN INDIRECT SOUECE OF THE FOOD OF FISHES. 759 



In the same article as previously quoted Woodward observes : "The 

 Cladocera are chiefly fresh water, and are distributed over the whole 

 world. Of this order the Daphnia pulexj so abundant in our [British] 

 fresh waters, is a good example. So numerous are they in our ponds in 

 summer as frequently to impart a blood-red hue to the water for many 

 yards in extent. In order to realize the wonderful fecundity of this and 

 allied genera, it is necessary to realize that when a Daphnia is only ten 

 days old eggs commence to be formed within the carapace, and under 

 favorable conditions of light and temperature it may have three broods 

 a month, or even a greater number, the larger species having as many as 

 forty or fifty eggs at once." 



The remarkable fecundity of theCopepoda explains the extraordinary 

 abundance of the free-swimming species upon the high seas, and even 

 bays, where vast schools of these crustaceans become, in turn, the food 

 of vast schools of herrings, menhaden, and shad. Doubtless, the move- 

 ments of these fishes on the high seas are determined by the abundance 

 of their favorite food in various localities; that, like the whale, they 

 seek their marine pasture of crustaceans, as argued by Mobius. Even 

 larger forms of fishes, such as the huge basking shark {Cetiorhinus max- 

 imns), have their branchial apparatus adapted to capture small pelagic 

 organisms in the same way as the Cluj^eoids. The prodigious numbers 

 of herrings and menhaden is a proof of the abundance of the minute 

 pelagic organisms upon which, with scarcely a doubt, it may be sup- 

 posed they subsist. It is also not improbable that the vast schools of 

 pelagic Entomostracans are in pursuit of still smaller protozoan prey, 

 upon which they subsist and maintain their marvellous reproductive 

 powers. Mosely, in his "Notes by a Naturalist on the Challenger," ob- 

 serves : " The dead pelagic animals must fall as a constant rain of food 

 upon the habitation of their deep-sea dependents. Maury, speaking of 

 the surface Foraminifera, wrote, ' The sea, like the snow-cloud, with its 

 flakes in a calm, is always letting fall upon its bed showers of micro- 

 scopic shells.'" Mosely records that he estimated, from experimental 

 data, that it would take four days and four hours for a dead Salpa to 

 fall to the bottom where the sea was 2,000 fathoms in depth. The deep- 

 sea fauna is probably well supplied with food from such sources. The 

 researches of Mr. John Murray, of the Challenger, fully confirm, and 

 greatly expand the significance of the views of Lieutenant Maury iij. 

 relation to the destiny of the marine foraminiferal shells. Wyville 

 Thompson, Voyage of the Challenger, I, 210, observes : " Mr. Murray 

 has combined with a careful examination of the soundings a constant 

 use of the tow-net, usually at the surface, but also at depths from ten to a 

 thousand fathoms ; and he finds the closest relation to exist between 

 the surlace fauna of any particular locality and the deposit which is 

 taking place at the bottom. In all seas, from the equator to the polar 

 ice, the tow-net contains GloMgerinw." Some of these surface Forami- 

 nifera are relatively large, OrhuUna nniversahQiugas much as a fiftieth 



