It 



■i\(;i; sKcxiSHKHO 



Statements 

 of frequenc}/. 



'lankton samples. 



Statements of 



locality, 

 istorical resumes. 



Final remark. 



joiiils, the figiiu'is abuvf tho lino ili'iiote tho ivlativc loiiglli of the joints on the dorsal or anteri(j)' 

 side, the figures below the line the rehitive length of tlie joints on the ventral or posterior side. 



I iniiv point out in passing that when I speak below of bristles that aic more or less 

 finely pectiuuted distally, this pectination is ])iesuinablv always in two rows, even if it is 

 shown in one ri»w in the drawing; the two rows of spines are often situated on the same si(U', 

 so that what is apparently one row of pectination seems to be present. This jjcctination could, 

 of course, only be reproduced in outline. 



It is often rather difficult to estimate the number of bristles because they are situated 

 so close together. G. W, MOller complains about this, 1894, p. 28 ... . „Wer die Schwierig- 

 keit einer genauen Feststellung dieser Verhaltnisse kennt . . . ." I think I have overcome 

 this «lifficulty, at least partly, by a simple manipulation: the limb (in glycerine) is crushed 

 by a slight pressure on the cover-glass and then the latter is moved, if desired, in different 

 tlirections. By this procedure bristles that are placed close to each other are sejjarated. I have 

 obtained very good results with this method. Chitinous parts ought not to be reproduced from 

 fresh material; the material ought first to be hardened in alcohol, or else the chitinous parts 

 are too strongly compressed by the cover-glass and misleading images arise. 



In the descriptions given in this work the penis is described rather superficially, 

 but I hope that the drawings that are given of this organ will, in spite of their being done in 

 outline, prove to be sufficiently detailed to permit of quite certain identification of species. 

 I hope to have an opportunity in a subsequent work to give more detailed descriptions and 

 reproductions of this organ which is so interesting from a morphological point of view. 



Although it is almost always stated below how many specimens of each species were 

 caught, this information cannot be used, except with very great caution, as an indication ol 

 the frequency of the forms in question, as the samples that were investigated were not collected 

 for comparative quantitive investigations. 



All the plankton samples were caught in open nets. The statements as to depth given 

 under these forms are consequently of comparatively little value. 



All statements as to the longitude of the localities are made with reference to Greenwich. 



A historical resimie is given after each of the higher systematic units, sub-families, 

 families, etc. These resumes deal chiefly with the historical development of our knowledge 

 of the classification of the Ostracod group and the organs that are most important for the 

 special classification, the shell, appendages, external sensory organs, etc. 



Before ending this introduction and giving the results of my investigations I wish to 

 quote a statement made by Th. Mortensen in his distinguished work on the Echinoids of the; 

 Ingolf Expedition, 1903, p. 3:,,Det viste sig, atDyrene var saerdeles gode 

 at have med at gore, Arterne meget vel karakteriserede. Det er 

 Literaturen, der bringer Vanskelighederne gennem den Uende- 

 lighed af daarlige Beskrivelser, den rummer."* This remark coincides 

 entirely with the experience I obtained myself in carrying out the present work. 



* Translation: The animals jirdved lo be very good \o work willi. Uie species were very well (lisliiif^iiislied. II is 

 the literature that causes difficulty on nceount of the great mmdier of ])oor descriptions it eontains. 



