xix GEOGRAPHICAL DISTRIBUTION 5 19 



Even this classification, which deals only with the larger 

 groups, must not be made use of without a word of warning. 

 The division of the Cheilostomata is a matter of great difficulty ; 

 and no scheme which has yet been suggested can be regarded as 

 more than tentative. The great number of forms included in 

 this group makes its subdivision extremely desirable from the 

 point of view of convenience ; but a further knowledge of the 

 anatomy and of the development of many of the forms of doubtful 

 systematic position is probably necessary before any scheme which 

 is likely to be permanent is put forward. Those who desire to 

 make a further study of the classification of the Polyzoa should 

 refer to the works of Hincks, 1 Busk, 2 MacGillivray, 3 and Gregory. 4 



The Polyzoa do not appear to lend any valuable assistance to- 

 wards settling the disputed problems of Geographical Distribution. 

 They are not in any case terrestrial, while the fresh-water species 

 do not always respect the limits between the great zoogeographical 

 regions. It has already been pointed out (p. 504) that Plumatella, 

 Fredericella, and Lophopus are believed to occur in Australia, and 

 the first-named genus is practically world-wide in its distribution. 



Many marine forms also have a surprisingly wide distribu- 

 tion. Thus among the British species which are described by 

 Mr. Hincks as occurring from Norway to New Zealand are 

 Menibranipora pilosa, Scrupocellaria scruposa, Cellaria fistvlosa, 

 Microporella ciliata, and M. malusii. Even if it should be 

 proved that specific differences do exist between the southern 

 forms and our own, there can be no doubt of the wide distribu- 

 tion of certain species. It was pointed out by D'Orbigny that 

 Bugula neritina has the habit of attaching itself to the bottoms 

 of ships, a fact which may possibly account for the wide distri- 

 bution of this species ; although it would not be safe to assume 

 this explanation of the facts in all cases. Other Polyzoa, on the 

 contrary, have a more restricted range. Thus Catenicella is 

 specially characteristic of the Australian region. 



It is perhaps surprising that marine Polyzoa should in so 

 many cases have so wide a range. Even though it is the rule 



1 Most of the writings of this author are referred to on pp. 277, 278 of Miss 

 Jelly's Synonymic Catalogue, referred to on p. 523. 



2 Catalogs of Marine. Polyzoa in the Collection of tlic British Museum, parts i.-iii. 

 1852-1875 ; and Challenger Reports, Parts 30 (1884) and 50 (1886). 



3 Trans, and Proc. R. Soc. Victoria, xxiii. 1887, p. 187, and Tr. . Soc. Victoria, 

 iv. 1895, p. 1. Tr. Zool Soc. xiiL 1895, p. 223. 



