634 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
r I he ovicells on the fossil forms have not escaped observation as D’Orbigny, 
Ilagenow, Keuss, and Pocta have figured them, although these students did not 
recognize their great value in classification. In 1897 1 Canu discovered the ovicell 
of the Melicerititidae, and in 1899 2 that of the Ceidae. In 1898’ 3 he published 
some special variations and indicated the great necessity for the study of the 
ovicell. In 1918 4 he published a summary of his new ideas on the classification 
of the Cyclostomata with descriptions of a number of new genera, a work which 
was preliminary to the present one where these ideas are more fully developed. 
GENERAL CONSIDERATION OF THE CYCLOSTOMATA. 
THE TUBES. 
The zooecia of the cyclostomatous bryozoa are tubular.. Whatever may be the 
zoarial form, each tube grows from a proximal tube by a special mode of gem- 
mation (fig. 196 A, B). 
Considering the form of the tubes there are : 
(a) Club-shaped tubes or typical Cyclostomata. 
(b) Cylindrical tubes or Cyclostomata resembling the trepostomatous bryozoa 
( c ) Tubes with facets. 
(cl) Tubes with rhomboidal orifice. 
This division, however, is not an absolute one. Hollow zoaria (in the Cavaria 
form of growth) often have shortened tubes the exact nature of which it is im- 
possible to determine. In the zoarium of Lichenopora , the polypidian tubes are 
club-shaped and the accessory tubes cylindrical. 
Considering their functions the tubes are classed as follows: 
(a) Polypidian tubes. 
(b) Accesory tubes (=aborted tubes of authors). 
(c) Adventitious tubes. 
The tubes are often grouped in longitudinal, transversal, or radial bundles 
(fascicles) which may be monoserial or pluriserial. 
Calcification. — The ectocyst is formed of two thin, flexible membranes between 
which the calcareous skeleton is located (fig. 196 C) 1 2 3 4 5 ; the tubes are therefore 
not strictly adjacent. The disappearance of the external membrane leaves a 
space which, in thin sections, appears as a clear line. This intercellular space is 
quite variable in size and is linear or vesicular. At the center of the agglomerate 
zoaria the tubes are often adjacent by reduction, reabsorption or filling up; rarely 
they are so in the entire zoarium (see Exochoecia) . 
1 1897. Canu, Bryozoaires du Turonien des Janitires, Bulletin Societe Gtiologique de France, ser. 3, vol. 
25, p. 155. 
2 1899. Canu, Les Ovicelles des C^idees, Bulletin Societe Geologique de France, ser. 3, vol. 27, p. 326. 
3 1898. Canu, Etude sur les Ovicelles des Bryozoaires du Batlionien d’Occaignes, Bulletin Societe 
GSoIogique de France, ser. 3, vol. 26, p. 259. 
4 1918. Canu. Les Ovicelles des Bryozoaires Cyclostoraes, Bulletin Societe Geologique de France, 
ser. 4, vol. 16, pp. 324-335. 
5 fOOO. Calvet. Contributions a l’histoire naturelle des Bryozoaires ectoproctes marins, Travaux In- 
stitut Zoologique University Montpellier Mem., No. 8, p. 160. 
