THE BRYOZOA — BASSLER. 353 



along the upper side while around the edge of the mass a zone of bud- 

 ding tissue gives rise to new zooids. Fredericella, another typical 

 genus, is a member of the deep-water fauna of the Swiss Lakes. 

 PlumateUco forms aggregations of parallel tubes. Lophopus and 

 Pectinatell-a., like Cristatelt-a, show powers of locomotion. These 

 genera have a wide geographical distribution, probably due to their 

 reproduction by statoblasts. They have been recovered from Europe, 

 North and South America, Africa, Australia, and other widely sepa- 

 rated areas. 



Although the species of Phylactolaemata are comparatively few, 

 they give rise to such interesting phenomena that the literature on 

 these fresh-water bryozoa is quite extensive. The monographs of 

 Allman 1X and of Jullien 12 should be consulted for a general review. 



Superorder GYMNOLAEMATA. ' 



As mentioned before, this superorder, characterized by the circular 

 row of tentacles surrounding the mouth only, is almost exclusively 

 marine and comprises most of the known recent bryozoa and practi- 

 cally all of the fossil forms. The body cavities are not continuous with 

 one another nor is the body wall muscular as in the Phylactolaemata. 

 In the majority of species, calcareous zooecial walls are deposited 

 and form very interesting objects of study. 



ORDER 1. CTENOSTOMATA. 



In this order the zooecia, which are frequentty isolated, are de- 

 veloped by budding from the internodes of a distinct tubular stolon 

 or stem, thus resembling to this extent the Entoprocta. Again they 

 unite laterally to form sheets, but in both cases the zooecial walls are 

 usually quite soft and uncalcified. The stolon is often threadlike 

 and gives off cjdindrical stalks, each of which dilates at its end into 

 the body of the zooid. The zooecial orifice is terminal and is closed 

 during retraction by an operculum of setae, which on account of its 

 resemblance to a comb, gives the name to the order (ctenos, comb). 

 All appendicular organs, such as avicularia, ovicells, and vibracula, 

 are wanting. In all the known forms the zooecia are membraneous, 

 and little capable of preservation. In some cases, fortunately, the 

 stolon becomes partially calcified and may thus be preserved fossil, 

 although all traces of the zooecium itself are lost. Then, again, 

 many of the Ctenostomata have the power of excavating a place for 

 themselves in the substance of the host they incrust, so that the size 



11 1856. Allman, G. J. A monograph of the fresh-water Polyzoa, Including all the known 

 species, both British and foreign. London, viii + 119 pp. 11 pis.. 



" 1885. Jullien. Monographic des Bryozoaires d'eau douce. Bulletin de la Society 

 Zoologique de France, X, pp. 01-207, 250 figs. 



42803°— 22 23 



