PLANKTONIC STUDIES. ; 601 
from the pelagic species of the surface by characteristic marks. “The 
wealth in such Alciopide (and Tomopteri de) at all depths of 100 meters 
or over is very surprising, and it requires a careful scrutiny, for the beau- 
tiful transparent worms often press actively by dozens in serpentine 
course through the crowd of other forms in the dishes” (15, p. 24). 
Crustacea.—In their general cecological importance, in their uni- 
versal distribution over all parts of the ocean, and especially in their 
incomprehensible fertility and the abundance of their appearance Ccon- 
ditioned thereby, the Crustacea surpass all other classes of animals. In 
the physiology of the plankton the first rank in the animal kingdom be- 
longs to them, as to diatoms in the vegetable kingdom. On the whole, 
in the organic life of the ocean they have the same predominant impor- 
tance as the insects for the fauna and flora of the land. In a similar 
way, as the complicated “struggle for existence” has called up for the 
latter a quantity of remarkable ecological relations and morphological 
differences conditioned thereby within the insect class, so has the same 
occurred in the ocean within the crustacean class. Meanwhile the 
numerous orders and families of this class, so rich in forms, participate 
in very different degrees in the constitution of the plankton. The order 
of ecopenods by far surpasses. all other orders. Next to these follow the 
ostracods and schizopods, then the phyllopods, amphipods and deca- 
pods. The other orders of crustaceans participate in the constitution 
of the plankton in a much less degree—part of them very little. It is 
to be added that larve of all orders may appear in great numbers 
therein. Thus, for example, the pelagic larve of the sessile benthonic 
cirripeds often appear in the neritic plankton so numerously that they 
constitute four-fifths to nine-tenths or even more of the entire mass. 
The chorology of the Crustacea offers to the plankton investigator one 
of the most important and interesting fields of work, the elaboration of 
which has yet scarcely been begun. The same applies also to the geog- 
raphy and topography of the oceanic and neritic Crustacea, both in 
their horizontal and vertical distribution, to their relations to the ben. 
thonic Crustacea as well as to the marine fauna and flora in general. 
Asa very important result of the recent discoveries, particularly of the 
Challenger, the fact must here as elsewhere be brought up that in the 
different groups of Crustacea (just as in the Radiolaria) the vertical 
divisions of the planktonic fauna can be very plainly distinguished. 
Pelagic, zonary, and bathybie forms are found here in quite definite 
relations. 
Copepoda.—As the Crustacea are on the whole the most important and 
influential among the planktonic animals in their cecological relations, 
so are the copepods among the Crustacea. Only one who has seen with 
his own eyes can gain a conception of the inmumerable masses in which 
these small crustaceans crowd the surface of the ocean as well as the 
zones of different depths. For days the ship may sail through wide 
stretches of ocean whose surface always remains covered with the same 
