ATLANT. DEEP-SEA EXPED. 1910. VOL. III]. 



PTEROPODA. 



41 



in the eastern part? Is this to be considered as merely 

 accidental, or as an expression of some unknown biological 

 relations of these animals? The total absence of some 

 species of Limacina in the eastern part of the open ocean 

 is all the more striking because the same species are found 

 abundantly represented along the African coastline. 



the Sargasso weed. Just at the place (Stations 51, 52) 

 where the "Michael Sars" first met with the Sargasso 

 weed, the three species of Limacina were also found for 

 the first time since leaving the Canary Islands, and they 

 were subsequently found distributed, sometimes in immense 

 numbers, all over the western part of the ocean. Is this 



O Limacina helicoides 

 9 Limacina lielicina 

 ^ Limacina balea 



€) Limacina retroversa 

 ® Limacina bulimoides 



Fig. 36. 



® Limacina lesueuri 

 ® Limacina inflata 



The hydrographical conditions at the time of the 

 expedition give no clue to the meaning of this distribu- 

 tion; there seems to be no reason why the animals should 

 not be able to live in the eastern part of the ocean as 

 well as in the western. 



One fact must, however, be mentioned which may 

 prove to be of interest in this connection, viz. the coin- 

 cident occurrence of the species of Limacina with that of 



coincidence merely accidental? or is there some causal 

 connection between the occurrence of the Sargasso weed 

 and that of the small species of Limacina? 



Such a causal connection might exist in one of two 

 different ways: either the animals in their development 

 or in their biology are in some way or other dependent 

 on the floating Sargasso weed, or the animals, like the 

 Sargasso weed, follow the currents running from the 



