8 Pratt, Marine Fauna of the Falkland Islands. 



P. tridentata differs from Jullien's P. malouinensis {see 

 Cap Horn Fxped.^ p. 57) in that the pores are larger and 

 fewer in number. P. fnalouinensis appears to have no 

 spatulate avicularium or denticles, and the secondary orifice 

 is somewhat different. The ovicell agrees with Jullien's 

 description of that in P. malouinensis, which, however, he 

 does not figure. 



A consideration of the geographical distribution of 

 the Bryozoa in this collection from the Falkland Islands, 

 is of special interest at the present time because of the 

 controversy about the origin of the north and south extra- 

 tropical marine faunas. 



Murray* is of opinion that "if there were once a nearly 

 universal climate over the whole of the ocean, then it is 

 possible that there was a universal littoral marine fauna." 

 When cooling set in at the Poles, then the animals with 

 pelagic larvae would be killed out, or be forced to migrate 

 towards the warmer tropics. By limiting their reproduc- 

 tive process to the summer season, some of the organisms 

 with free swimming larvae would live on in the temperate 

 regions. With the disappearance of the shallow-water 

 fauna from the polar regions, its place would be occupied 

 by organisms from the deeper mud line, few of which have 

 pelagic larvae. In this way the similarity and, in some 

 cases, identity between the polar faunas, and the likeness 

 of many shallow- water polar animals to deep-sea species, 

 might be explained. 



The cooling of the waters at the Poles would cause vast 

 migrations of forms towards the warmer seas, where 

 metabolic changes would be greater; this would cause the 



* Murray ' ' On the Deep and Shallow-water Marine Fauna of the 

 Kerguelen Region of the Great Southern Ocean." {Trans. R. Soc. Ed., 

 Vol. 38 (1896), p. 343 ; also Challenger SiLmmary of Results.) 



