﻿COPEPODA 



(Canu 1892), but thc:r structure is quite different from the one described; lately I have examined the 

 labrum and labium in two genera of the Hurpactolda^ in Oncaca and in Oif/iona. but only in the 

 latter genus found a structure not quite dissimilar to the one described. 



In the nauplius of Ca/aiiux I have not yet succeeded in elucidating the structure of these or- 

 gans; in the first postlarval stage of C. /iin/iarchicits the structure is in its main feature like that of 

 the adult one. 



The structure of the mouth organs in the males is, in species in which the oral appendages 

 are not reduced, scarcely different from that of the female, but in otiier forms, it is more or less 

 reduced (cf. pi. IV fig. i e; pi. YI fig. 3 e). 



From the above it seems to me to be evident that the study of these organs in different forms 

 is of no mean importance. 



On postlarval development. 



Most modern authors, who have studied the I'lancton-Copepods from the systematic point of view 

 have only paid attention to the adult males and females, even when younger specimens were present; in 

 later years Oberg has given a description of the larval stages in several species and Kraeeft has paid 

 much attention to the postlarval development in a very interesting paper; Dam as, Paulsen and 

 Stephensen have for single species contributed to our knowledge of the development. It is generall\' 

 understood that G rob ben is the first who has described the nauplius in Calainis /iin/iarciiiciis and 

 that Gran was the first to give an account of the postnauplial development; both statements are wrong, 

 as Kroyer, as early as the year 1847, followed the development of Calaims /iin/iarchicus from the 

 nauplius to the adult (or more correctly the penultimate stage). In this paj^er I have not dealt with 

 the larval forms, but I have tried and generally succeeded in determining the postlarval stages; 

 1 have named the first postlarval form stage I, and the adult male and female stage \'I. About the 

 differences between the different stages in each species, and the reductions in the limbs I refer to the 

 systematic part; the most complete account is found in the description of Cal. fiinitarclucns. The 

 mouth-organs are generally not reduced in the Stages IV — V; the number of setae in the exopoditc 

 of the maxillulae forms an exception to this rule. In the adidt female the number is 11, in stage 

 V it is 10, in stage IV it is 9, in stage III it is 8, in stage II it is 7 and in stage I probably 6. 

 The main differences between the stages is found in the number of natatory legs and number of 

 somites of the urosome. 



Nomenclature. 



In the naming of the different appendages I have followed Hansen as well as Giesbrecht, 

 who .somewhat later arrived at the same residt. Hansen has shown that the tvitciiiiai\ iiunidtbiilae 

 and maxillipcds really have threesegmented basipodites. The structure of the xiaxilliihu- in Valdivirlla 

 insignis shows clearly, that the basipodite of these limbs are threesegmented: the first basal segment 

 is adorned with the U I; the second bears the Le and a single Li (II ^ HI); the third ba.sal .segment 

 which is distinctly articulated to the preceding one, supports the tvo rami. The natatory legs ap- 



