248 



REPORT ON THE PENNATULTDA. 



is some considerable distance below the margin of the calyx, while in 

 the fully expanded fourth polype the mouth is seen to be some distance 

 above the calyx margin. 



The mouth leads by a narrow oesophageal passage into the thick- 

 walled stomach (u), which is thrown into folds closely similar to those 

 of Funiculhia or Peiuiatula. The concertina-like action of these folds 

 as the polype is expanded or retracted is well shown in Fig. 5 ; in the 

 retracted polype the folds of the stomach are closely pressed together, 

 and the whole stomach is very short : when, on the other hand, the 

 polype is protruded, the folds of the stomach-wall are pulled out, and 

 the whole organ becomes at least double its jirevious length. 



As in the other two genera the stomach-wall consists of a thick 

 inner lining of ectoderm cells, a thin mesodermal layer, and a fairly 

 thick outer coat of endoderm cells continuous with those lining the 

 body-cavity. 



e. The Mesenteries, like those of FunicuUna and Fennatula, are eight 

 vertical partitions or septa, uniting the body-walls and stomach 

 together, and extending below the latter down to the bottom of the 

 polype-cavity. 



Round the stomach the mesenteries are arranged at nearly equal 

 intervals, two being attached to the upper surface of the leaf, two to 

 the lower, and two to each of the partition walls separating the polype 

 from its neighbours on either side. Below the stomach the arrange- 

 ment becomes asymmetrical, in the manner already described as 

 occurring in Fennatula ; i.e., the two mesenteries attached to the 

 upper surface of the leaf retain their position, or even move slightly 

 away from one another, while the lateral ones shift downwards 

 towards the lower surface. This change of position is well shown in 

 the two lower sections of Fig. 7, which show also that while the upper 

 two mesenteries remain of some width the whole way down the polype, 

 the other six become very soon reduced to mere ridges. 



The arrangement of the muscles in the mesenteries is the same 

 as in the other two genera. The strong retractor muscles (j)), by which 

 the polype and tentacles are withdrawn into the calyx and the folds of 

 the stomach approximated to one another, are shown in the several 

 polypes of Fig. 5. 



/. The Mesenterial Filaments. — Here again the arrangement is 

 closely similar to that of FunicuUna or Fennatula ; as in these genera, 

 there ai'e in each polype six short mesenterial filaments (Figs. 5 and 7 r), 

 which are thickenings on the edges of the lateral and under pairs of 

 mesenteries, and which, commencing at the lower end of the stomach, 

 only extend a short way down the polype cavity ; and two long mesen- 

 terial filaments, formed on the edges of the upper pair of mesenteries 

 (Figs. 5 and 7 s), and extending down quite to the bottom of the polype 

 cavity. All the mesenterial filaments are much convoluted, and the 

 two long ones are much thicker than in either of the other two genera. 



We have obtained evidence concerning the digestive function of 

 these mesenterial filaments of a precisely similar nature to that already 



