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; Avails thin, minutely porous; apertural por- 
tion of zooecial tubes more or less raised, bent outAvards, free or in bundles. 
Marsupia and appendicular organs wanting. Ovioell 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. TO, 71) can lie 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 shoAving on the zooecium. 
The value of the ovicell in the classification of the Cyelostomata is therefore of 
utmost importance, but unfortunately until A-ery recently its study has been much 
neglected. 
The most important work on the ovicells of recent species is that of. Waters, 
published in 189I 2 and Ibid 3 . In 1893 4 the remarkable phenomenon whereby 
a single egg can engender a considerable number of larvae was discovered by 
Harmer. This discovery of the fissiparitv of the primary embryo explains the 
rarity of ovicells. 
1 Catalogue Fossil Bryozoa in Department of Geology, British Museum, .vol. 2, pp. xxiv-xli. 
2 1894, AA^aters, Ovicells of Cyclostomatous 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. . 
884-836. 
1 1893. Harmer, Embryonic Fission in Cyclostomatous Bryozoa, Quarterly Journal of Miscroscopicai 
Science (n. s.), vol. 34, pp. 199-241, pis. 21-24. 
633 
