58o 



DEPTHS OF THE OCEAN 



surface of the animals and facilitate their floating, while in northern 

 waters the species are devoid of such appendages. It is thus interesting 

 to compare the widespread species Calanus finmarchicus (Fig. 416), 

 which occurs in greatest abundance in boreal areas, with the tropical 

 Augaptiliis filigeriis (Fig. 417), which has elaborate appendages, reminding 

 one of peacocks' feathers. We find the same difference between 

 Oithona plumifera and Oithona similis, and between EiicJiczta marina 

 and Euclmta norvegica (Fig. 418). We find in these cases a perfect 

 analogy with what Gran has 

 described among the peridineae 

 in Chapter VI. ; for instance, 

 Ceratiuni platycorne (see Fig. 

 228, p. 324) in warm water en- 



FiG. 417. 



Augaptilus filigerus, Claus. 

 (After Zacharias, from Steuer. ) 





Fig. 418. 



/ iichata norvegica, Boeck. 



( From Sars. ) 



larges its surface, while in cold 

 water the horns are much more 

 slender, the lower specific gravity 

 caused by the higher temperature 

 rendering floating appliances 

 necessary for both animals and plants (see also Chapter X.). 



The Copepoda occur in all depths, and some authors have attempted 

 to define certain bathymetrical regions, each with its own characteristic 

 forms, but the observations available are insufficient to enable us to 

 form definite ideas on the subject ; much new light will' doubtless be 

 thrown on the matter when the reports of the " Valdivia" and " Michael 

 Sars " Expeditions come to be published. The discussion as to whether 

 the surface forms of cold regions are found in the deep water of warm 

 regions is interesting. 



The " Valdivia " Expedition captured EucJiirella venusta and Calanus 

 finmarchicus in a haul with a closing net between 1600 and 1850 metres 



