PREFACE. 



The present Volume deals with one of the great divisions of the ex- 

 tensive order, Copepoda, viz., that of the Calanoida, which of late has attracted 

 the special interest of biologists, on account of the enormous numbers in which 

 some of the species are sometimes found to appear, forming, as they do, a very 

 essential part of the so-called Zoo-plankton. As not only the amount of the 

 plankton, but also its quality is of great significance in determining the nutritive 

 value of the water both in the sea and in lakes, a thorough knowledge of the 

 organisms composing it may be said to be quite indispensable. It is now gener- 

 ally admitted that Copepoda of the Calanoid group form an essential part of the 

 nourishment of several of our common food-fishes, either in the adult state, or 

 at any rate in the earlier periods of their life; and the investigation of- these 

 little creatures must therefore be regarded as intimately connected with that of 

 the fisheries, whether in the sea or in lakes. 



The present Volume, which gives full diagnoses and figures of all Nor- 

 wegian Calanoids, both marine and fresh-water, known at present, may thus, I 

 hope, be of essential use to those who are studying our fisheries and the biological 

 conditions connected therewith. 



In order to make the determination of the species as easy as possible, 

 I have given, besides anatomical analyses, carefully drawn habitus-figures of all, 

 in most cases both a dorsal and a lateral view, and as a rule of both sexes. 

 The detail figures, unlike those in Dr. Giesbrecht's work, are always arranged in 

 such a manner, that they can at once be referred to their respective species. 



An objection may perhaps be urged against the practical arrangement of 

 the present Volume, as also of the 3 preceding Volumes, viz., that no analytical 

 tables are given. In my opinion, however, the practical value of such tables, 

 especially when they comprise a great number of different forms requiring a more 

 or less complicated arrangement, has been much overestimated. I think that the 



