PLANK TONIC STUDIES. 601 



from tlu' pelagic species of the surface by characteristic marks. ^'Tbe 

 wealth ill such Alclopidw (and Tomopteridw) 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. 21). 



Crustacea. — In their general (ecological importance, in their uni- 

 versal distribution over all parts of the ocean-, and especially in their 

 incomprehensible fertility and the abundance of their apjiearance con- 

 ditioned thereby, the Gnisfacca surj)ass 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 liredominant 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 au'ological 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 f;imilies of this class, so rich in forms, participate 

 in very different degrees in the constitution of the plankton. The order 

 of coj)epods 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 larv?e of all orders may appear in great numbers 

 therein. Thus, for example, the pelagic larv.ne 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 i)lankton 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 horizoutal and vertical distribution, to their relations to the ben- 

 thonic Crustacea as well as to the marine fiiuna and flora in general. 

 As a very important result of the recent discoveries, particularly of the 

 Clinllenger, the fact must here as elsewhere be brought up that in the 

 different grou])s of Crustacea (just as in the Radiolaria) the vertical 

 divisions of the planlctomc fauna can be very plainly distinguished. 

 Pelagic, zonary, and bathybic forms are found here in (juite definite 

 relations. 



Copepoda. — As the Crustacea arc 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 innumerable 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 remai us covered with the same 



