CXVl INTRODUCTION. 



Mediterranean, Madeira, Sontli America, Australia, New 

 Zealand. Caber ea Buryi has a wider range. These are in 

 no measure abyssal forms (which are generally very widely 

 diffused), but flourish between tide-marks and in shallow 

 water, though also found at greater depths. There are many 

 facts in the distributional history of the Polyzoa of which 

 it is difficult to find an adequate explanation. In addi- 

 tion to migration along the coast-lines and through the 

 profound depths, which are subject to uniform climatic 

 conditions, there has been a more irregular and sporadic 

 diffusion by the agency of cm^rents, floating weed, timber, 

 &c., and by means of ships. Probably the latter may 

 have played a not unimportant secondary part in deter- 

 mining some of the more abnormal phenomena of distri- 

 bution. Many of the species exhibit great adajjtabilit}'^ 

 to different climatic conditions, and if transported to 

 distant regions might readily accommodate themselves to 

 their new home. 



Glancing at the foreign relations of our native species, 

 Ave find a very close resemblance between the Polyzoan 

 fauna of the south-west coasts of France and of our own ; 

 of 53 species recorded by Fischer 45 or 4G are British. 

 A small group is common to our shores and to those of 

 South Africa : the species composing it are in great 

 measure very widely distributed forms ; and almost all of 

 them are also Mediterranean. Of the species (about 30) 

 Avhicli are both Madeiran and British, almost all are essen- 

 tially southern forms : most of them have been recorded 

 as Mediterranean; and probably all will prove to be so. 

 One or two northern intruders {Scrupocellarla scabra &c.) 

 occur amongst them. Australia and New Zealand have 

 each a fcAV species that belong to our fauna ; and of 



