POLYZOA. 91 



which the undigested part of their food is finally ejected ; 

 this opening is surrounded hy a number of prehensile 

 tentacula capable of a remarkable degree of extension and 

 contraction ; in their growth they resemble plants, push- 

 ing out branchings and ramifications, each branchlet 

 forming a complete individual ; they appear to be entirely 

 divested of any regular system of organs, circulating, ner- 

 vous, or generative. 



The Naturalists who have subsequently most contributed 

 towards the knowledge of these Hydrae, are Bernard de 

 Jussieu, Guetard and Donati ; but it is undoubtedly to Ellis 

 we are under the greatest number of obligations for the 

 length to which he prosecuted their natural History, and 

 the descriptions and figures with which he has enriched 

 this branch of knowledge. 



Later investigators threw no new light upon these 

 animals, so that Naturalists were satisfied of the identity of 

 the animal inhabitant, and of the propriety of assimilating 

 them in one connected group or Class, since however, that 

 it has been deemed necessary to examine more minutely 

 into the anatomical structure of animals, these notions 

 have been disturbed by the discovery made by Renier in 

 1793. (Opusc. scelt. torn. 16 ^j. 256 t. \.) that the animals 

 of the Botryllus Stellatus were not Hydrae but Ascidise, and 

 consequently appertaining to the MoUusca acephala, 

 animals of a much higher Order, having a distinct res- 

 piratory organ, a mouth distinct from the Anus, a stomach, 

 intestinal canal, ovaria, &c. It was reserved to ]\Ions. 

 Savigny however in 1815 and 16 to demonstrate that 

 numberless Linnaean Alcyonii possess analogous animals 

 with the Botryllus Stellatus. * To these important dis- 



* Mem. snr les animaux sans vertebres. Ihe designs which accompany 

 the first of these Alemoirs, M. Savigny says, were executed in 1810 and the 

 Memoirs made known to the institute in February 1815. Subsequently Messrs. 

 Desmarets, jun. and Le Sueur (to whom these discoveries must have been 

 knowu) analysed Avith equal success the animals of the Botryllus Stellatus and 

 of the Pvrosoma. 



