VIROULARIA MIRABILIS. 07 



d. The Stomach. — Tlie mouth, as shown iu Fig. 5, m, is situated on 

 the apex of a small papilla that rises up in the middle of the circle of 

 tentacles, the outer wall of the papilla being continuous with the bases 

 of the tentacles and the inner with the wall of the stomach. The 

 mouth is a transverse slit (Fig. 7), whose long axis is at right angles 

 to the flat surface of the leaf. The varying position of the mouth in 

 different conditions of protrusion or retraction of the polype is well 

 shown in the several polypes of Fig. 5. When the tentacles are 

 completely retracted, as in the second and seventh polypes, the mouth 

 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 nari'ow cBsophageal passage into the thick- 

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

 of Funiculina or Pennutula. The concertina-like action of these folds 

 as the polype is expanded or retractel 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 previous 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 FunicttUna and PennatuJa, 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. 



Eound 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 Pennutula ; 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 

 polj'TJes of Fig. 5. 



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

 closely similar to that of Funiculina or Pennatuln ; as in these genera, 

 there are in each polype six short mesenterial jilanients (Figs. 5 and 7 ;), 



