PLANKTONIC STUDIES. 609 



and imiform plankton when this exceeds three-fourths and forms ahuost 

 the whole mass. 



In general the mixed plauktou is more abundant than the simple, 

 since as a rule the circumstances of the "struggle for existence" condi- 

 tion and vary in many ways the constitution of the plauktonic flora and 

 fauna. Still there are numerous exceptions to this rule, aiul at many 

 points in the ocean (especially in the zoocurrents) there occurs locally 

 a development so numerous, and an accumulation of a single form or 

 group of forms in such swarms, that these in tlie haul of the -pelagic net- 

 form more than one-half the entire volume. This monotonic planlxton 

 appears in very different definite forms; for the difference of climate, 

 tlie season, the oceanic currents, the neritic relation, etc., determine 

 significant differences in the quantitative development of the plankton 

 organisms, whicli simultaneously appear iu vast numbers in a defiiute 

 region. I Avill next briefly go over the single forms of the monotonic 

 plankton known to me, passing over, however, the consideration of the 

 extremely manifold composition of the poJi/micic plankton, since I am 

 reserving that as well as a contribution of a number of mixture-tables 

 for a later work. 



1. Monotonic Frotopliytic Plankton. — Of the seven grou])s of pelagic 

 Protophi/tes, ;it least three, the Diatoms, Murraaytes, and Feridinea', 

 appear in such qriantities in the ocean that they alone may constitute 

 the larger part of the collection of the pelagic nets. The most impor- 

 tant and most common is the monotonic diatom-plankton, particularly in 

 brackish and coast waters, Tlie siliceous-shelled unicellular Protophijtcs 

 whicli compose this belong, often predominantly or almost entirely, to 

 a single species or genus, as Syncdre in the colder, Chwtoceros in the 

 warmer seas. The colossal masses of Arctic and Antarctic diatoms, 

 which form the "black- water," the feeding-ground of whales, have been 

 mentioned above. In the warmer tropical and subtropical parts of 

 the ocean such accumulations of diatoms seldom or never occur. Here 

 tlieir i)lace is taken l)y the monotonic murracyte-plankton, composed of 

 immense swarms of nyctipelagic Pyrocystidce. Less frequent is the 

 monotonic pcndinca'-plankton. Although these Dinofiagellata take a 

 very significant part in the composition, especially of the neritic plaidc- 

 ton, yet they do not often occur in such quantities as to form the 

 greater part of the volume of the capture. 



2. Monotonic Metaphytic- Plankton. — Among the pelagic Metaphytes 

 there are only two forms, the Oscillator im and the ^argassav, which 

 appear so numerously that they form the greater part of the pelagic 

 tow- stuff'. The monotonic oscillator ia'-plankton, as a rule formed of 

 swimming buiulles of fibers of a single species of Trichodcsminm, ap- 

 pears in many regions of the tropical ocean iu such masses that the 

 quantity of the pelagic fauna is diminished on that account. The 

 monotonic saryassiim-pl<(nkton. formed of ''swimming l)anks" of a single 

 fucoid, Saryassion Oacci/enan, is the (characteristic massive tbrm of 

 organic life iu the Halistasa of the " Sargasso Sea." 



H. Mis. 113 39 



