198 REPORT ON THE PENNATULIDA. 



5. — Anatomy of the Zooida. — 



The zooids of Pennattila, like those of Funiculina, differ from the 

 polypes ill the follow iug structural points, besides the difference in size 

 and position already noticed : — 



1. Though there is a well-developed stomach, and as a rule a 

 mouth as well, there are no tentacles or calyx. 



2. All eight mesenteries are present around and supporting the 

 stomach, but only two of the eight have their free edges below the 

 stomach thickened to form mesenterial filaments. The two mesen- 

 terial filaments present extend down to the bottom of the body cavity 

 of the zooid, and clearly correspond to the two long slender filaments 

 of the polypes. 



3. The zooids liave no reproductive organs. The walls of the 

 zooids are very thickly studded with calcareous spicules, and the lower 

 ends of the zooid cavities communicate freely with the spongy canal 

 system of the wall of the rachis. At least two thirds of the length of 

 the zooid is embedded in the wall of the rachis, so that it is only by 

 making sections of the rachis that the anatomy of the zooids can be 

 ascertained. The smaller zooids have no mouths, and are therefore 

 dependent for their nutriment on the supply brought by the canal 

 system from the polypes. 



Zoological Position and Affinities — 



The general position of Pennaiula in the order FennatuUda is shown 

 in the table on page 1 of this report. The generic characters, as given 

 by KoUiker,* are as follows : — 



"Genus : Pennatula — True Sea-pens, with well developed leaves, in 

 which there are no zooids and no very large calcareous rods + but a 

 number of small spicules. Zooids situated along the whole ventral 

 surface of the rachis, and also on the lateral surfaces between the 

 leaves. Polypes in cups, beset with calcareous spicules ; calyx 

 processes variable in number." 



KoUiker distinguishes four species of Pennatula, whose leading 

 characters are as follow : — 



1. Pennatula pliospliorea. Leaves formed of single rows of polypes, 

 eight to eighteen in number, eight calyx processes to each polype ; 

 reproductive organs contained in the leaves. 



2. Pennatula rubra. Leaves formed of single rows of polypes, 

 twenty-five to forty-six in number, placed alternately, so as to give 

 appearance of double rows. Calyx processes usually three or four to 

 each polype ; reproductive organs confined to the parts of the leaves 

 within the rachis. 



3. Pennatula borealis. Large pens, up to thirty-two inches long ; 

 leaves thick, formed of two to four rows of polypes. 



4. Pennatula fimbriata. Leaves formed of two rows of polypes. 



* KoUiker : Op, cit., p. 12:2. t As in Pteroeides, e.g. 



