PLANKTONIC STUDIES. 609 



and uniform planUon when this exceeds three-fourths and forms ahnost 

 the whole mass. 



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

 since as. a rule the circumstances of the "strug-o-le for existence" condi- 

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

 fauna. Still there are numerous exceptions to this rule, and 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 the haul of the pelagic net 

 form more than one-half the entire volume. This monotonk' planldon 

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

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

 significant differences in the quantitative development of the plankton 

 organisms, which simultaneously appear in vast numbers in a definite 

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

 l^lankton known to me, passing over, however, the consideration of the 

 extremely manifold composition of the pohjmixic planlcfon, since I am 

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

 for a later work. 



1. Monotonic rrotoplnjtic PlanMon.—Oi the seven groups of pelagic 

 Protophytcs, at least three, the Diatomic, Miwracytes, and Peridinew, 

 appear in such quantities 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-planMon, particularly in 

 brackishand coast waters. Tlie siliceous-shelled unicellular Profophi/fcs 

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

 a single species or genus, as Syncdrc in the colder, Chwtoceros in tlie 

 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 

 their place is taken by the monotonio murraciite-planUon, composed of 

 immense swarms of nyctipelagic Pyrocystidw. Less frequent is the 

 monotonic pcridinexv-pJanUon. Although these THnofiageJlaia take a 

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

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

 greater part of the volume of the capture. 



2. Monotonic Mefaphytic-Planlcton.— Among the pelagic Metaphytes 

 there are only two tbrms, the Oscillatoriw and the Saroassew, which 

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

 t<jwstuff. The monotonic osciUatonw-planlcton, as a rule formed of 

 swimming bundles of fibers of a single species of TricJiodesmium, ap- 

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

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

 monotonic saygassnm-planlcton, formed of "swimming banks" of a single 

 fucoid, Saryassum baecifernm, is the characteristic massive form of 

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

 H. Mis. 113 39 



