278 HINCKSj ON THE CHEILOSTOMATOUS POLYZOA. 



and the remaining side AC^ may be determined. In the 

 latter triangle, ACD, there will now be known the angles 

 and the side AC ; whence the sides AD, DC may be found. 



It will be for practice to determine with what amount of 

 rigour the indications of theory will require to be carried out. 

 And it may be worth while to remark, finally, that the pencil, 

 as emergent from the object-glass and incident on the prism, 

 is not strictly parallel ; but it would serve no useful purpose 

 to take account of the slight amount of convergency it 

 possesses. 



Note on the Ovicells of the Cheilostomatous Polvzoa. 

 By the Rev. Thomas Hincks, B.A. 



(Read at the British Association, September, 1861.) 



Most of the Cheilostomatous Polyzoa (Polyzoa furnished 

 with a moveable lip, which closes the mouth) exhibit at certain 

 seasons external capsules, of various forms, which are situated 

 generally at the upper extremity of the cells, and overarch 

 the orifice. It has long been known that in these ovicells 

 ciliated embryos are matured, which, after making their 

 escape and passing through a free existence of longer or 

 shorter duration, become fixed and are developed into 

 the perfect Polyzoon. A question has been raised, how- 

 ever, as to the birthplace of the ova which originate these 

 motile embryos, and Professor Huxley has adopted the 

 theory that they are produced within the cell itself, either 

 in an ovarium attached to the side of the cell-wall 

 (endocyst), or on the cord (funiculus) which in some 

 species connects the body of the polypide with the bottom of 

 the cell. He supposes (or did suppose in 1856, when his note 

 on the subject was communicated to the ' Microscopical 

 Journal,^ vol. iv, p. 191), that the ova, after impregnation in 

 the perigastric cavity, pass into the ovicell, and " there, as in 

 a marsupial pouch," undergo their further development. 

 In the same paper Professor Huxley remarks that " the 

 general idea, that the ova are developed within the ovicells," is 

 " wholly an assumption." 



This very plausible conjecture has been virtually accepted 

 as the true explanation of the function of the Polyzoan ovi- 

 cells, and has not been challenged, so far as I am aware, in 

 any published work. My object in this notice is to give a 

 brief account of observations which I have made on the deve- 



