568 



POLYZOA. 



Fani. 1. Cristatellidae. Free-moving colonies, on the upper surface of which 



the zooids are arranged in concen- 

 tric ellipses. Cristatella Cuvier. 



Fam. 2. Plumatellidae. At- 

 tached, massive or ramified colo- 

 nies of fleshy or coriaceous con- 

 sistency. Pcctinatella Leidy ; 

 Lophopus Dumortier, discovered 

 by Trembley in 1741, and is the 

 first Polyzoon of which we have 

 any notice ; L. crystallinus Pall. ; 

 Plumatella Lamk., including Al- 

 cyonella Lamk., A. fungosa Pall.; 

 P. repens L. (Fig. 452) ; Frederi- 

 cella Gervais, differs from the other 

 members of the family in having 

 a nearly circular lophophore ; the 

 statoblasts are without a ring of 

 air-cells. 



FIG. 452. Plumatella repens slightly magnified 

 (after Allman). Lp lophophore ; D alimentary 

 canal. 



t 



t 



Class II. ENTOPROCTA. 



Anus within the tentacular circlet. 



The Entoproda are more simply organised than the Edoprocta. 

 The tentacular circlet surrounds a kind of vestibule into which the 

 mouth and anus, the gener- 

 ative and excretory organs 

 open. The alimentary canal 

 is a simple U-shaped tube, 

 differentiated into oesophagus, 

 stomach, and rectum (Fig. 

 453). There is a ganglion 

 in the floor of the vestibule 

 between the mouth and anus. 

 There is no body-cavity, but 

 only a slight amount of con- 

 nective tissue between the 

 body-wall and gut-wall. There 

 is a pair of fine, ciliated canals, 

 which are described by some 

 observers as intracellular, by 

 others as intercellular, which, 

 lie on the ventral face of the 

 stomach and open into the 



vestibule on the oral side of 

 the ganglion. 



FIG. 453. Diagrammatic longitudinal section 

 through Pfdicellina (after Ehlers, from Kor- 

 schelt and Heider). a anus ; ep epistome ; ex 

 excretory canal : g gonad ; m, mouth ; ms fibres 

 of the circular muscle ; n ganglion ; t tentacles. 



