CRUSTACEA COFEPODA- 



CHAP. 



in the species figured, Calocalanus plumulosus (Fig. 26), from the 



Mediterranean. 



Sars makes a curious observation 1 with regard to the 



distribution of certain Calanidae. He reports that along the whole 



route of the "Fram," 

 species such asCalanvs 

 hyperboreus and JSuclt- 

 aeta norweyica were 

 taken at the surface, 

 which, in the Nor- 

 wegian fjords, only 

 occur at depths of over 

 100 fathoms. He 

 suggests that the Nor- 

 wegian individuals, 

 instead of migrating 

 northwards as the 

 warmer climate super- 

 vened, have sought 

 boreal conditions of 

 temperature by sinking 

 into the deeper waters. 



Fn:. 26. Calocalanus plumulosus, x 15. 

 (After Giesbrecht. ) 



TRIBE II. 



HETERARTHRAN- 

 DRIA. 



The first antennae 

 of the male are asym- 

 metrical, one, usually the right, being used as a clasping 

 organ. 



The males of the Centropagidae, Candacidae and Pontellidae, 

 besides possessing the asymmetrically modified thoracic limbs of 

 the fifth pair also exhibit a modification of one of the first 

 antennae, which is generally thickened in the middle, and has 

 a peculiar joint in it, or geniculation, which enables it to be 

 flexed and so used as a clasping organ for holding the female. 



Fam. 1. Centropagidae. These Copepods are very common 

 in the pelagic plankton, and some of the species vie with the 



1 Norwegian North Polar Exp. Sei. Results, vol. i. part v., 1900. 



