325 



ments alhided to by Trembley correspond closely with fas- 

 ciculi described above, as existing in paludicella, and which 

 I have also witnessed in other fresh water zoophytes ; and I 

 cannot but think, notwithstanding the high authority of 

 Raspail, that they are really such as Trembley desci'ibes 

 them. It is worth remarking, that Raspail denies the exis- 

 tence of retractor muscles in alcyonella, believing that, with 

 the general contractility of the animal, such a contrivance 

 would be superfluous. I have not yet succeeded in obtaining 

 any specimens of alcyonella, so that upon this point I cannot 

 speak from direct observation. Since these muscles, how- 

 ever, are particularly well marked in all the fresh water 

 ascidian zoophytes, whose anatomy I have studied, as well 

 as in those of the ocean, I must still adhere to the original 

 observation of Trembley -, for it can hardly be supposed, that 

 a genus so nearly allied to those in which the system in 

 question is well developed, and which Raspail, by the way, 

 would consider but as a different grade of evolution, should 

 be altogether destitute of them. 



" In Pluraatella repens I have examined, with much care, 

 the retractor apparatus. In this species it consists of two 

 fasciculi of muscular fibres, which arise from the sides of the 

 cell near the bottom ; and thence passing upwards symmetri- 

 cally, one along each side of the body of the polype, receive 

 an extensive attachment, being inserted into the wide part of 

 the tentacular crescent, into the pharynx for its entire length, 

 and into the upper part of the stomach ; a few fibres appear 

 detached at each side from the main fasciculus, to be inserted 

 more externally near the base of the tentacular lobes. The 

 function of these muscles is evident, acting from their more 

 fixed attachment to the side of the cell, they become power- 

 ful retractors, by which the body of the polype is drawn 

 inwards and concealed in the more internal parts of the poly- 

 pidom. 



" In the~opercular muscles, paludicella offers no remark- 



