Order CYCLOSTOMATA Busk. 



Zooecia very simple, cylindrical, calcareous tubes arising from a proximal tube 

 by some special mode of gemmation, usually without transverse partitions; orifice 

 plain, inoperculate, not contracted; walls thin, minutely porous; apertural por- 

 tion of zooecial tubes more or less raised, bent outwards, free or in bundles. 

 Marsupia and appendicular organs wanting. Ovicell an enlarged zooecium or 

 an inflation of the zoarial surface. 



Hitherto the families and genera of Cyclostomata have been founded almost 

 entirely upon the form of the zoarium and the arrangement of the zooecia. 

 Various classifications have been proposed, but it is needless to review them here 

 because Gregory in 1909 1 gave a good account of them and discussed the general 

 problem of classification at some length. 



The distinction between the families of Cyclostomata, like the other orders, of 

 Bryozoa, is or should be based on their larval forms, each family being chara- 

 terized by a special larva. The larvae of the Cyclostomata are very similar to 

 each other and difficult to discriminate, but fortunately they show their differences 

 by the evolution of the embryos in ovicells of very different size, form, and 

 position. 



We believe that the same principles of classification as are applied to the 

 apparently more complicated Cheilostomata (see pp. 70, 71) can be employed in 

 the study of the Cyclostomata. indeed, that a natural classification can be built 

 up by a study of the physiologic functions of the organs. In the Cheilostomata 

 it will be noted that the form of the aperture and of the operculum, the presence 

 of the cardelles, occurrence of lyrula and the ovicell were the essential characters 

 of generic and family classification. In the Cyclostomata the aperture is always 

 more or less circular, the operculum, cardelles, and lyrula are wanting, leaving 

 the ovicell as the single remaining essential character showing on the zooecium. 

 The value of the ovicell in the classification of the Cyclostomata is therefore of 

 utmost importance, but unfortunately until very recently its study has been much 

 neglected. 



The most important work on the ovicells of recent species is that of Waters, 

 published in 1894 2 and 1914 3 . In 1893* the remarkable phenomenon whereby 

 a single egg can engender a considerable number of lai'vae was discovered by 

 Harmer. This discovery of the fissiparity of the primary embryo explains the 

 rarity of ovicells. 



1 Catalogue Fossil Bryozoa in Department of Geology, British Museum, vol. '2, pp. xxiv-xli. 



! 1894. Waters, Ovicells of Cyclostoroatous Bryozoa, Linnean Society Journal, vol. 20, pp. 275-285, pi. 

 14, 15. 



3 1914. Waters, The marine fauna of British East-Africa, Proceedings of the Zoological Society, pp. 

 834-836. 



1 1893. Harmer. Embryonic Fission in Cyclostomatous Bryozoa, Quarterly Journal of Miscroscopical 

 Science (n. s.), vol. 34, pp. 199-241, pis. 21-24. 



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