with descriptions of some new species. 355 



sui-face of the polypidom clean. I can confirai from personal 

 obsenation the remarks which some authors have made respect- 

 ing the force with which the movements of these hair-like appen- 

 dages are executed. 



Membranipora pilosa. 



The polypes of this common species are furnished with a sin- 

 gular organ, which has been described by Dr. Farre in his admi- 

 rable paper on the Ciliobrachiata. It consists of a small ob- 

 long body, which is placed between the base of two of the arms, 

 and attached to the tentacular ling. It has a wide cii'cular 

 opening at the top, round which there is a play of cilia. The 

 interior ca\ity is lined with cilia. The organ becomes naiTow 

 towards the base, and is closely united to the sides of the ten- 

 tacles. Dr. Farre noticed a similar body on the poh-])es of Al- 

 cyonidium gelatinosum (Johnston). He states that he was un- 

 able to detect any flow of fluids through it, nor could he ascer- 

 tain with what parts the cavity in its interior might commu- 

 nicate. I had long made this organ the subject of close investi- 

 gation mthout gaining any clue to its histon,- ; but at length 

 some Hght was thrown upon it by the following observations. 

 Specimens of the zoophj-te were procured in the spring, in which 

 the cercaria of Dr. Fan-e — ^filamentous bodies which are found 

 swimming in the visceral cavity in many species of Brjozoa — were 

 present in great abundance. They were also of larger size than 

 any I had previously met with. In one of the polypes I obseiTed 

 a mass of these cercaria wiiggling upward from the lower part of 

 the visceral cavity ; and each filament, when it reached the base 

 of the organ before referred to, was di-awn into it and earned 

 through it by the action of the cilia lining the interior, and then 

 ejected and borne ofi" by the tentacular currents. This expulsion 

 went on for three or four minutes, during which time the fila- 

 ments were streaming up incessantly from below. A great quan- 

 tity was ejected. After a while a single filament only made its 

 appearance occasionally, and at last none were to be seen. 



Dr. Farre mentions that on one occasion he observed the cer- 

 caritB in a specimen of Alcyonidium " drifting rapidly to the upper 

 part of the \isceral caWty, and issuing from the centre of the 

 tentacula," but from the sudden retraction of the polype he lost 

 the opportunity of tracing their course. He adds, "it would 

 appear from this that there is some external communication with 

 the cavity of the body." My observations show that this com- 

 munication is through the intertentacular organ, and that what- 

 ever pui'pose it may subserve beside in the CEConomy of the Bry- 

 ozoon, it is at certain seasons the channel through which cercarue 

 are ejected from the visceral cavity. The author before quoted 



23* 



