324 



pass upwards to be inserted into the fundus of the stomach. 

 It is true, that Trembley describes in alcyonella stagnorum, a 

 certain appendage to the fundus of the stomach, to which he 

 assigns the office of a retractor muscle; " J'ai vu," says Trem- 

 bley, " distinctement, lorsque les polypes a panache etaient 

 bien au dehors de leur cellules un fil qui tenait d'un cote a 

 I'extreraite inferieure de I'estomac et de I'autre au fond dela 

 cellule."* Raspail supposes this an erroneous observation, 

 and conceives that Trembley mistook for a distinct organ, 

 the appeai'ance presented under the microscope, by a fold 

 of the reflected tunic.f Notwithstanding, however, the criti- 

 cism of Raspail, I believe the observation of the celebrated 

 historian of the green polype to he perfectly correct, though 

 his reasoning is erroneous. 



" 1 have myself witnessed in Pluraatella repens, an organ 

 in every respect corresponding to Trembley's description; I 

 believe this organ to be an ovary, though from its position 

 and attachments, Trembley's opinion might at first appear 

 correct, and the structure in question might be supposed 

 analogous to the posterior set of retractor muscles in the 

 ciliobrachiate zoophytes of the sea. This supposition, how- 

 ever, is untenable, and I have satisfied myself by repeated 

 observations, that no such function is performed by it; it is 

 observed to undergo no contraction, and its motions are en- 

 tirely passive and dependant on those of the body of the 

 polype. 



" In the same animal, Trembley also describes as retractor 

 muscles, filaments attached by one extremity to the base of 

 the plume of tentacula, and by the other to the bottom of 

 the cell ;$ but this, likewise, is considered by Raspail as an 

 error, and referrible to the same source as the former. Here 

 again I must dissent from the French naturalist ; the fila- 



* Hist, des Polypes d'Eau douce, p. 216. 



t Mem. de la See. d'Hist. Nat. de Paris, torn. 4, p. 92. 



J Op. cit. p. 216. 



