Alcyonella. Z. ASCIDIOIDA. 315 



The Alcyonella, if I have correctly sorted the synonynaes, was disco- 

 vered by Trembley in the spring of 1741. It seems necessary to give a 

 copy of his figures here, (wood-cut, No. 48,) since on them is founded 

 the second variation of the species, and they exhibit it in a guise very 

 different from that represented in our Plate xliv. His history of the 

 animal is marked with much of that excellence which distinguishes 

 the inquiries of this naturalist. He correctly describes the connec- 

 tion and relationship between the polype and the common mass ; the 

 arrangement of the tentacula, and the structure of the alimentary 

 canal, although he failed to detect the anus. He overlooked the 

 cilia of the tentacula from employing magnifiers of too low a power, 

 and attributed the whirlpools created in the water by their play to 

 the motion of the tentacula themselves, which he says were also used 

 separately to force the aniraalcular prey into the mouth. He knew 

 that the polypes were not contractile, and believed their retraction 

 within the tubes was dependant on the play of a muscular thread 

 which descended from the body in the common mass. The gemmi- 

 parous mode of increase in the polypidom is also detailed with some 

 minuteness, but he had not seen the ova, at least in a state of ma- 

 turity.* 



Immediately after Trembley's discovery, Reaumur and Bernard de 

 Jussieu found this animal in the neighbourhood of Paris, and detect- 

 ed its ova, from which they saw the young issue. Reaumur's ac- 

 count of the growth of the compound animal appears to me to cor- 

 roborate the opinion of the sameness of the Plumatella and Alcyonella. 

 He says that while the polypes a panache are still very young, they 

 increase in the same manner that the locomotive polypes do, with 

 one difference only which it is essential to note, since it explains 

 clearly the formation of those polypidoms that resemble plants. The 

 tube of a newly evolved polype continues as it were permanently 

 grafted upon the tube of that which has given birth to it : from the 

 polype tube he has seen germinate by little and little another which 

 contained a nascent polype ; he has seen this tube elongate itself, and 

 the polype tenant at length show itself outwards to follow out the 

 destined tenor of its life. Scarcely had a few days passed until this 

 again gave birth to a young one whose tube was in connection with 



* It is even doubtful whether the bodies he took for imviature ova were 

 really so. " J'ai vu dans plusieurs des Polypes a panache, sur lesquels j'ai fait 

 mes obser\-ations, de petit corps spheriques de differentes grandeurs, blancs et 

 transparens. J'ai seulement soup(;onne que ces petits corps etoient des oeufs, 

 mais je n ai pas eu occasion d'cxaminer si ce soup9on etoit fonde, ou non. ' p. 

 219. 



