358 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1020. 



dorsal side of many branching forms is sometimes occupied by 

 short tubes called nematopores, which appear at the surface as 

 thread-like and in thin sections as narrow tubes upwardly directed. 

 Somewhat similar tubes on the dorsal side grow in the opposite 

 direction — that is, toward the zoarial base. These are the firmMo- 

 pores. Certain Cyclostomata exhibit pores on the dorsal side as 

 large as the polypide tubes, but with polygonal orifice. These 

 are termed "tergoporesP Somewhat similar pores on the frontal 

 side, but covered by calcareous closures, are known as dactyl^thrae, 

 while cancelli, another curious development on the frontal side, are 

 cylindrical tubes closed by a finely perforated lamella and gar- 

 nished in the interior with numerous spinules. Still other forms 

 of tubes in this order are the ramifications of the polypidian tubes, 

 termed "vacuoles" and " mesopores." The physiologic function of 

 these various accessory tubes is still unknown, but they are constant 

 in their development and are therefore of value in classification. 

 Plate 4 exhibits the aspect of these various tubes both at the surface 

 and in thin sections. 



The method of division or gemmation of the zooecial tubes in the 

 Cyclostomata is also quite important. In one method (peripheral) 

 the tubes bifurcate at all heights and in all directions. In another 

 method (oriented) gemmation occurs in a definite manner on a 

 single or on two sides of a basal lamella or of an axial zone. Thin 

 sections here again are indispensable in the study of this order. 



Although many researches upon the Cyclostomata have been pub- 

 lished, comparatively little attention has been devoted to the anatomy 

 of the polypide, the study of its method of protrusion, and to the 

 larval forms in addition to the ovicell. So far as known the ovicells 

 contain numerous embryos, which have arisen by fission of a primary 

 embryo developed from an egg. 



The Cyclostomata commence in the Middle Ordovician and con- 

 tinue until the end of the Paleozoic era fairly well developed in 

 number but of less importance than the two strictly Paleozoic orders, 

 Trepostomata and Cryptostomata. In the Early and Middle Meso- 

 zoic they constitute the predominating order, but in the Creta- 

 ceous the Cheilostomata assume first place and continue so until 

 the present. The Paleozoic forms have been described by Ulrich 

 and other workers mentioned under the Trepostomata. The Meso- 

 zoic species have been the subject of numerous publications among 

 which may be mentioned those by Gregory 18 and by D'Orbigny. 19 

 The Cenozoic Cyclostomata likewise have received much attention, 

 as will be noted by consulting the monograph by Canu and Bass- 



18 Gregory. Catalogue of Fossil Bryozoa in British Museum, Jurassic (1896), Cretaceous 

 vol. 1, 1899, and Cretaceous vol. 2, 1909. 



19 1852. D'Orbigny. Paleontologie francais, Terrain Crgtace, Vol. V. 



