574 



DEPTHS OF THE OCEAN 



-^.4 



'V 



deep-living forms. Among surface forms only Pelagia perla was taken 



abundantly, and its distribution was peculiar, the species being most 



numerous along the line of stations crossing the Azores in a north and 



south direction, coinciding 



with the submarine ridge \\ 



on which these islands are : 'W^.. 



situated (see Map III.). 

 Siphono- The Siphonophores are i 



phorae. an interesting group, .. - -^ 



sometimes referred to the i ^^ 



hydromedusae, but entirely I 



independent. They are 



oceanic, and have no 



bottom - stage, their de- 

 velopment being a direct 



one. This class of animals 



is exceedingly rich in 



species, and we can only 



mention some North 



Atlantic forms. 



Only three species are 



wholly indigenous to 



northern waters : Diphyes 



arctica (Fig. 407), peculiar 



to the Gulf Stream north 



of lat. 59° or 60'^ N., ex- 

 tending to Spitsbergen in 



lat, 81° N., and Galeolaria 



biloba and Cupiilita cara, 



which are less common. In 



the Atlantic we find a 



wealth of both deep - sea 



and pelagic forms, some of 



the latter being known as 



visitors in the North Sea 



and the Norwegian Sea, a 



few having being found on 



the west coast of Norway 



and described by Michael 



Sars as long ago as the 



'thirties, like Agalmopsis 



elegans and Physophora hydrostatica (Fig. 408) ; in the Sognefjord 

 Haeckel also found Circalia stephanomvia. These forms have numerous 



swimming bells and long tentacles, and are interesting as immigrants 



from the Atlantic into the North Sea and the Norwegian Sea, Among 



forms peculiar to the warm surface layers we may mention the 

 " Portuguese man-o'-war," Physalia aretJmsa (Fig, 409), and the " By 

 the wind sailor," Velella spiralis (Fig, 410), which belong to the regions 

 south of the 40th degree, but have occasionally been found as visitors on 

 the shores of the British Islands. 



Physoplu 



Fig. 408. 

 ■a hydrostatica, Forskal. 



About half iiat. 



(From M. Sars.) 



