VEEMES. 65 



Class VII. POLYZOA. 



BRYOZOA. CILIOBRANCHIATA. POLYPIARIA. CELLULIFERA. 

 TENTACULIPERA. TENTACULIBRANCHLE. 



Associated, mostly marine animals, each living in a cell on a 

 plant-like organism, or adnate upon foreign bodies, very rarely 

 free. Mouth surrounded with ciliated tentacles. Hermaphro- 

 dite. A metamorphosis. 



The separate animals or zooids are called "polypides" or 

 "persona}," the entire system is a "zoarium," also " polyzoarium " 

 or " coancecium," and the "zooacium," or cell, is the organ in 

 which the polypide is contained. The tentacles are borne on a 

 projection or stage called the " lophophore." The alimentary 

 canal " is suspended in a double-walled sac." There is a single 

 nerve-ganglion placed between the mouth and the anus, which are 

 very near together. There is no vascular system, nor any sense- 

 organ. The animals do not communicate with one another as 

 they do in the hydroid polypes [Calyptoblastea]. There is, how- 

 ever, said to be a general system of nerves by which the polypides 

 are placed in communication. 



Reproduction is by ova, the young appearing in the form of a 

 free ciliated sac-like body ; and by continuous gemination, each 

 new zooid remaining attached, and adding to, the parent-stock. 

 Another form of gemmation, confined, however, to the Pbylacto- 

 laemata, occurs in which certain bodies, called "statoblasts," are 

 developed in the polypide ; these are enclosed in two horny disks, 

 and "when the statoblasts are placed under circumstances favour- 

 ing their development, they open by the separation from one 

 another of the two faces, and then there escapes from them 

 a young Polyzoon, already in an advanced stage of development, 

 and in all essential respects resembling the adult individual in 

 whose cell the statoblasts were produced" (Attmari). 



Much difference of opinion exists as to the affinities of the Poly- 

 zoa. Ehlers considers that their nearest allies are the Gephyrea ; 

 Claus places them between the Nernatoid worms and the Rotifera ; 

 Barrois also insists on their intimate relations to Rotifers. Von 

 Hayek (1877) unites the two orders Bryozoa and Roiaioria to 

 form his Ciliata, the sixth and last class of Vermes. They have 

 also been held to constitute a lower form of Tunicata ; but then, 

 as has been observed, no Polyzoon begins life as an Ascidian, and 

 no Ascidian begins life as a ciliated gemmule ; and if, as Hancock 



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