MEMBRANIPOEA. 329 



It is oblong, placed between the base of two of the arms, 

 and attached to the tentacular ring. Eound the opening at 

 the top there is a play of cilia, and it is lined with cilia. 

 Mr. Hincks had long made this organ the subject of inves- 

 tigation, and at length he was rewarded by the following 

 discoveries. '' Specimens of the zoophyte were procured 

 in spring, in which the cercaria of Dr. Tarre — filamentous 

 bodies which are found swimming in the visceral cavity in 

 many species of Bryozoa — were present in great abundance. 

 In one of these polypes I observed a mass of these cercarice 

 wriggling upward from the low^er part of the visceral cavity ; 

 and each filament, when it reached the base of the organ 

 before referred to, was drawn into it and carried through 

 it by the action of the ciha lining the interior, and then 

 ejected and borne off by the tentacular currents. This ex- 

 pulsion went on for three or four minutes, during which 

 time the filaments were streaming up incessantly from below. 

 After a while a single filament only made its appearance 

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



Dr. Parre having observed the cercarice in Alcyoniunij 

 " drifting rapidly to the upper part of the visceral cavity," 

 adds, " it would appear from this that there is some external 

 communication with the cavity of the body." Mr. Hincks 



