108 Dr Grant on the Struciure and Nature of Plustra, 



mode of generation of Flustrae, with sufficient detail, either to 

 comprehend the history of a single species, or to determine the 

 true nature of the genus. The most accurate observers ha^e 

 unfortunately confined their observations to the skeleton, while 

 those who had opportunities of examining the soft parts, in the 

 living state, have been blinded by preconceived hypotheses, and 

 their observations are neither minute nor correct. The accurate 

 and minute observations of Ellis and Pallas relate solely to the 

 axis. Easterns examined these animals frequently alive on the 

 coasts of Holland, and often saw the ova moving to and fro 

 spontaneously on escaping from the cells ; but, as he maintained 

 that the polypi of all zoophytes are merely species of vermin 

 infesting the surface of aquatic plants, he naturally considered 

 these moving bodies, both in flustrae and in other zoophytes in 

 which he likewise observed them, as polypi which had left their 

 habitations, to swim about for a time in search of prey, and 

 again returned to their cells. Spallanzani observed the polypi 

 bent like a bow in their cells, and supposed them connected to 

 the cells by their lower extremity ; he remarked the bell-shaped 

 arrangement of the tentacula around the mouth, and the con- 

 stant currents towards that orifice, — ^but he did not perceive the 

 ciliae placed on the two lateral margins of the tentacula, and 

 imagined the currents to be produced " by the constant agita- 

 tion of the arms."' The same function has been erroneously 

 ascribed to the tentacula by most authors, and the number of 

 these organs in any species has not been accurately ascertained. 

 A very slight observation is sufficient to shew that the cells of 

 flustrae are more isolated than they are in most zoophytes, and 

 tlmt the lower part of the polypus is not continuous with a cen- 

 tral fleshy axis, as it is in Sertulariag, Plumulariae, Campanula- 

 riae, and many other keratophytes. This circumstance early led 

 to an opinion that the polypi of flustrae have no connection with 

 each other, and that the whole substance consists only of a con- 

 geries of independent cells. This opinion was strengthened by 

 the statement of Laefling, that, when one polypus of the F. pi- 

 losa is touched, the neighbouring polypi are not affected, and 

 that, in advancing from their cells, they advance without order 

 or regularity. It is likewise stated by the same observer, that 

 the new cells, placed around the margins of the branches, arc 



