PLANKTONIC STUDIES. 601 



from the pelagic species of the surface by cliaracteristic marks. "The 

 wealth iu such Alciopidw (and Tomopteridce) at all depths of 100 meters 

 or over is very surprising, and it requires a caveful scrutiny, for the beau- 

 tiful trauspareut worms ofteu press actively by dozens in serpentine 

 course through the crowd of other forms in the dishes'' (15, p. 24). 



Crustdcea. — In their general <Pcoh)gical importance, in their uni- 

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

 incomprehensible fertility and the abundance of their appearance con- 

 ditioned thereby, the Gnistacea surjDass 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 lias the same 

 occurred in the ocean within the crustacean class. Meanwhile the 

 numerous orders and families of this class, so rich in forms, partici[»ate 

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

 of copepods by far surpasses all other orders. ISText to these follow the 

 ostracods and schizopods, then the phyllopods, amjdiipods 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 larvic of all orders may appear in great numbers 

 therein. Thus, for example, the pelagic larvje 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 horizontal and vertical distribution, to their relations to the ben 

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

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

 Challengerj the fact must here as elsewhere be brought up that in the 

 different groups of Crustacea (just as in the Eadiolaria) the vertical 

 divisions of the planMonic fauna can be very plainly distinguished. 

 Pelagic, zonary, and bathybic 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 innumerable masses in which 

 these small crustaceans crowd the surface of the ocean as well as the 

 zones of different depths. For days the sliip may sail through wide 

 stretches of ocean whose surface always remains covered with the same 



