564 POLYZOA. 



The actual process of budding appears to be similar to the process 

 by which the first polypide arises from the primary zooecium, that is 

 to say the budding polypide is derived from a two-layered vesicle 

 attached to the inner side of the body-wall of the parent zooecium. 

 The inner wall of this vesicle is formed from the ectoderm, and 

 gives rise to the alimentary canal, ganglion, and covering of the 

 tentacles and tentacle-sheath of the new form, while the outer wall 

 constitutes the mesodermal structures of the new polypide. The 

 endoderm does not take part in the gemmation of the Ectoprocta. 



Class I. ECTOPROCTA. 



Anus outside the tentacular circlet. 



This group includes by far the greater number of the Polyzoa, 

 and their structure has been specially referred to in the precedent 

 description of the class. The anus always opens outside the ring 

 of tentacles, which are either arranged in a circle (Gymnolaemata) 

 or on a two-armed horseshoe-shaped lophophore The coelom is 

 well developed, and the reproductive cells are developed from its 

 lining. 



Order 1. GYMNOLAEMATA. 



Ectoprocta with circular lophophore, without epistome. 



The Gymnolaemata are, with a few exceptions, marine forms. Alcyonidium 

 and Hoivcrbaukia are found in estuaries, and Victorclla and Paludicella are only 

 known in fresh or brackish water. Statoblasts are never found ; but in the 

 fresh-water forms the whole colony dies down in the winter with the exception 

 of certain external buds, which are called hibernacula and give rise in the spring 

 to new colonies. 



The ciiticle is sometimes horny, and sometimes encrusted with calcareous 

 matters, over which a layer of cells may even extend. The zooecia present 

 a great variety of form. 



Sub-order 1. CHEILOSTOMATA. 



The orifice of the zooecium can be closed by an operculum. Avicularia, vibra- 

 cula, and ovicells are often present. 



Tribe A. CELLULARINA. With corneous or corneo-calcareous infundibuli- 

 form cells, the inferior part of which below the aperture is tubular or obconic. 



Fam. 1. Aeteidae. 'Zooecia tubular, with a lateral membranous area; 

 orifice terminal. Tentacle-sheath terminating above in a circle of setae, which 

 are everted during the expansion of the polypide. Actea Lamouroux. 



Fam. 2. Eucrateidae. Zooecia uniserial, or in two series placed back to 

 back, with a terminal or subterminal and usually oblique aperture. Avicularia 

 and vibracula absent. Zoaria as slender, branching, phytoid tufts. Eucratea 

 Lamx. ; Gemellaria Sav. ; Scruparia Hincks ; Huxlcya Dyster ; Bretiia Dyster ; 

 Pasythea Lamx. 



