92 MEMOIR V. 



coverics may be added those made by Le Sueur (Tratis. 

 Acad. Nat. Sciences of Philadelphia, Vol. 1. p. 176 t. viii.) 

 that the animals of various Madrepores, of the Genera 

 Caryophyllea, Astrea, Meandrina, &c. possess a considera- 

 bly more complicated structure than Hydra, and one more 

 nearly approaching to that of Zoantha and Actinia. 



These several discoveries while they point out the dis- 

 similar structure of the animal in the Zoophites, open a 

 vast field for exploration. 



The present Memoir has for its object to demonstrate 

 another form of animal not hitherto known, and which 

 while it must be allowed to belong to a new type of the 

 Mollusca acephala, resembles exteriorly in some measure 

 the Hydra, this animal has been designated by the name 

 of Polyzoa, because it appears to be quite peculiar to the 

 compound animals, and unlike Hydra, Actinia and Ascidia 

 has never been observed in a single and separate state. 

 The Polyzoa will probably be found in many dissimilar 

 Genera of the Zoophites, and even mixed up with Hydra 

 in some, as they appear to be in the Sertularia of authors, 

 and hence this discovery must be the cause of extensive 

 alterations and dismemberments in the Class with which 

 they have hitherto been associated. Thus this discovery 

 will rremove that portion of the Sertularia not provided 

 with distinct oviferous receptacles, to the class Mollusca 

 acephala, as well as such other genera as may hereafter be 

 found similarly circumstanced. I shall merely indicate 

 liere in a general way the whole of the Flustraceffi, in many 

 of which I have clearly ascertained the animals to be 

 Polyzose. 



If amongst the Genera of the class of Zoophites, there 

 is one which resembles a vegetable production in general 

 appearance, roots, rapidity of growth and limited duration, 

 more than any other, it is certainly that of Sertularia, a 

 family so admirably illustrated by Mr. Ellis in his Natural 



