MEMBRANIPORA. 127 



The avicularia in this family almost always exhibit a 

 more highly specialized form than in the preceding. They 

 are usually secondary formations, borne upon the zocccia 

 instead of being developed in the same plane with them. 



In a great proportion of cases the colonies in the 

 present family, and indeed very commonly amongst the 

 Cheilostomata at large, originate in a peculiarly shaped 

 cell, which differs widely from the mature zooecium. 

 And these primary cells exhibit, with minor differences, 

 a general similarity of structure. They are for the most 

 part somewhat rounded, with a large terminal aperture, 

 closed in by a membrane, and usually surrounded by a 

 number of spines. Such a form was long since described 

 by Van Beneden as a distinct genus, under the name of 

 Tata*] and the original cell of the Cheilostomatous colony 

 is often distinguished as the Tata-form. Of course this 

 genus, being founded on an early and immature condition, 

 which is common to a large section of the Polyzoa, has 

 not been maintained. I have designated the first element 

 of the Cheilostomatous colony the primary cell ; and if a 

 separate name is needed for the form which it generally 

 assumes, it may be styled the T^a-stage. 



Genus MEMBRANIPORA, Blainville. 



Der. From memoir ana, a thin akin, and ponts, an opening. 



ESCIIARA (part.), Pallas. 



FLUSTRA (part), Linn. : Lamarck : Fleming : Lamouroux : Audouin. 

 MEMBRA.XIPOHA, Blainville, Man. d'Actinol. : Johnston: Busk: Suiitt: ice. 

 DISCOPORA (part.), Laink. An. . V. 



* " Recherche* ur le> PoL Brjozoairw de la mer du Nord," Bull. Ac. 

 Roy. Belg. xri. no. 12 (1849), p. 



