PENNATULA PHOSPHOREA. 41 



I 



As shown in the second section of Fiij. 5, the proti-actor muscles are 

 situated on one face only of the mesenteries, and a comparison of this 

 figure with Fijj. 13 of Plate II. will show that the actual arrangement 

 is the same as in Funiculiiia. The two upper mesenteries, which bear 

 below the stomach the long mesenterial filaments, and are situated on 

 the left-hand side of both the figures referred to, have the retractor 

 muscles on the sides facing away from one another ; the two opposite 

 mesenteries, those on the lower surface of the leaf and the right-hand 

 side of the figures, have the retractor muscles on the sides facing one 

 another, while the intermediate or dorsal and ventral mesenteries bear 

 the muscles on their right-hand sides in the figures. 



It is clear therefore that, as in Funiciilina, there is only one bisecting 

 plane that will divide the polype into two perfectly symmetrical halves, 

 and it is also evident from Figs. 3 and 5, and from the description given 

 above that the platie of .■fi/mmetrn is perpendicular to the flat surface of 

 the leaf, and is therefore the plane of section adopted in Fig. 4. 



The retractor muscles pull back the bases of the tentacles, and at 

 the same time shorten the stomach, as described above, so as to make 

 room for them ; the completion of the retraction of the tentacles is 

 effected by their own intrinsic system of longitudinal muscles ; 

 and the final action of the great retractor muscles is by pulling on the 

 bases of the calyx processes to bring these towards one another and so 

 completely close the mouth of the polype cup. 



/. The Mesenterial Filaments. — -The mesenterial filaments, which 

 are simply the thickened edges of the mesenteries below the stomach, 

 fall as already noticed into two groups ; a set of two situated on the 

 upper surface of the leaf and extending down to the bottom of the 

 polype cavities, the long mesenterial filaments (Figs. 4 and o s) ; and a set 

 of six, the short mesenterial jilami'nts, Figs. 4 and 5 r, which only 

 extend a short way below the stomach. 



The long mesenterial filaments have the same character along the 

 whole of their length : they are straight, or very slightly convoluted, 

 and are in transverse section (Fig. 5 s) bifid, the filament and 

 mesentery together having the appearance of a letter Y with very 

 thick arms. Each arm consists of a thin stratum of connective tissue, 

 clothed on its upper surface — that towaz-ds the upper surface of the 

 leaf — by a thin layer of flat epithelial cells, and on its under surface by 

 a single layer of elongated columnar ciliated cells, which are granular 

 in appearance, and possibly in part of glandular natui-e. Concerning 

 the function of these long mesenterial filaments we know nothing. 



The short mesenterial filaments, Figs. 4 and .5 r, are, like those of 

 Funiculina, thick and much convoluted. They are rather shorter than 

 those of Ftuiiculina, being not quite so long as the stomach in its ex- 

 panded condition, and their length is the same in all the polypes of 

 the leaf, however long or short these themselves may be. They com- 

 mence about the spot where the polypes become free from one another, 

 so that the greater part or the whole of their length is contained in 

 the leaf proper. 



