PLANKTONIC STUDIES. 627 
on the trip, Richard Greeff, has described the Canary animal streams 
so vividly that I will here give his description verbatim: 
Our gaze was directed to the highly peculiar long and narrow ecnrrents, which 
are of very especial importance for pelagic fishery with fine nets. If one looks at 
the calm sea, especially from an elevation over a wide expanse of water, here and 
there are seen strongly marked shining streaks, which intersect the surface as long 
narrow bands. Their course and place of appearance seem to be continually chang- 
ing and irregular. Sometimes they are numerous, sometimes only few or entirely 
absent; to-day they appear here, to-morrow there; some have one direction, others 
the opposite or crossing the first. Occasionally they run along close to one another 
and unite in a single stream. If one approaches this streak it becomes evident 
that here in fact a current prevails different from the movements of the surrounding 
water, and that thereby is brought about the smooth band-like appearance. They 
give the impression of streams cutting through the rest of the ocean, with their own 
channel and banks, which, notwithstanding the great variations in the time and 
place of their appearance, yet during their existence, which is often brief, show a 
certain independence. 
If one comes upon such streams, which are not too far distant from the coast, he 
sees. that all the smaller, lighter objects which formerly scattered over the surface, 
floated about or cast upon the shore, were drawn into it. Pieces of wood and cork, 
straw, algw, and tangle torn loose from the bottom, all in motley procession are carried 
along in this current. But in addition (and this is for us the most important 
phenomenon) all the animals belonging in the region of these currents are drawn in 
and fill it, often in such great quantities that one is tempted to believe it is not 
merely the mechanical influence of the narrow stream which has brought about such 
an accumulation of animals, but that the latter voluntarily seek out these smooth, 
quiet streams, perhaps in connection with certain vital expressions. A trip upon 
such a pelagic animal road furnishes a fund of very interesting observations. We 
can lean over the edge of the boat and review the countless brightly colored sea- 
dwellers, sometimes passing by singly, so that we can inspect them in their unique 
peculiarities, sometimes in such thickly massed hordes that they seem to form an 
unbroken layer of animals for afew feet below the surface. Yet these animal roads, 
where one meets them in the sea, will always form the most certain and richest 
mine for the so-called pelagic fauna, although naturally, from their changeableness 
and their dependence upon a calm sea, they can never be definitely counted upon. 
Likewise, the origin of these noticeable streams and their significance in the natural 
history of the sea is still almost completely dark, in spite of the fact that they can 
be observed in almost all seas and under favorable circumstances daily, and also are 
known to the fishermen of Arrecife under the name Zain (18, p. 307). 
Although the zoécurrents seem to occur in the most diverse parts of 
the ocean, and have often aroused the astonishment of observers, yet a 
recent investigation of them is wanting. What I know about them 
from my own experience and from the contributions of others is 
essentially the following: 
The zodcurrents occur in the open ocean as well as in the coast 
regions, particularly in the region of those nerocurrents which run in 
straits between islands or along indented coasts. They are dependent 
upon the weather, especially the wind, and appear as a rule only dur- 
ing calms. Although in the case of the neritic zodcurrents the local 
course is more or less constant, still it is subject to daily (or even 
hourly) variations. Their breadth is usually between 5 and 10 meters, 
but sometimes 20 to 30 meters or more; their length is sometimes only a 
