Miscellaneous. 309 



the principal scp:racTit of the polyp-cell. Lastly, the ventral septula 

 have still shorter and thick filaments, and the septula arc continued 

 as far as the extremity of the ventral diverticula of the body-cavity. 



11. The U.ruaJ oir/ans are seated only on the four lateral septula, 

 occur only in fully developed polyps, and in other respects are as 

 in the other Pennatulida). 



12. The rv/Iimentnry 2'>oT.)jps or zooids arc seated upon the dorsal 

 surface of the disk, in groups of from five to thirtj^ or forty together. 

 Each group possesses in its interior a common cavity, and on the 

 surface as many small cavities as there are zooids ; and in each of 

 these there are eight Tory small septa without mesenteric filaments. 

 The common cavity of each group opens by a round aperture into 

 the main cell of a polyp or into its dorsal diverticulum. 



13. Around the groups of zooids a variable number of spines are 

 often seated. It is a matter of more interest that in certain species 

 one zooid regularly possesses simple tentacles on two compartments, 

 which serve to represent the lateral ventrals ; these represent the 

 calycino tentacles of the sexually mature polypes, and are generally 

 supported by two spines. The zooid bearing these two tentacles is 

 also usually larger 'than the rest. 



14. The aquiferous pore described by Fritz Miiller in the middle 

 of the frond of the ReniJla; is the orifice of an isolated large zooid 

 possessing a stomach and eight septa, but no plumose tentacles, fila- 

 ments, or sexual organs, and somewhat resembling, in size and the 

 spines surrounding it, the sexually matiire animal. The body- 

 cavity of this " chief zooid" opens into the end of the dorsal sinus 

 of the keel. 



15. The polyp-cells are lined with epithelium, muscles, and con- 

 nective tissue ; and these muscles produce the extraordinarily 

 strong extensions and contractions of which the frond of ReniJla is 

 capable. 



16. The spknles of the ReniUce are all essentially of the same 

 form (see my ' Icones histiol.'), and, after the extraction of the calca- 

 reous salt by acids, leave a coloured organic residue of exactly the 

 form of the previous structure. — Proc. of the Phys.-med. Gesellschaft 

 in Wiirzburg, Feb. 4, 1871. 



Observations on Urnatclla, a Genus of Ciliated Poh/j^s of the Family 

 Pedicellinida>. By Prof. Leidy. 

 This polyp is found abundantly below the dam at Fairmount, in 

 the Schuylkill River, adhering to stones and rocks, on the sides and 

 underpart not in contact with the ground. Occasionally it is 

 observed attached to the shell of the liAring Unio complanatus and 

 MeJania virginica, and less frequently to the stem of Schollera f/ra- 

 minea and the leaves of VnUisneria spiralis. In the locality named, 

 on the rocks, there may bo observed, in association with Urnatella, 

 the following animals •.—SponijiJla fraf/ills, Limnins ceratophylli 

 (usually abundant and in compound bunches), Cofhurnia pusilla 

 (parasitic on Urnatella and Limnias), Hydra camea, Ag., Palvdicella 



