FUNICULINA QUADRANGULARIS. 15 



polype (Fif?. 10;)), by which tlie stomach can be drawn down, and the 

 tentacles pulled back within the calyx. 



Each retractor muscle, as shown in Fig. 10, extends the whole 

 length of the septum to which it belongs. Arising from the body- 

 wall along the whole length of the base of attachment of the 

 septum, the fibres pass up in bundles in the substance of the septum, 

 and are inserted inaiuly into the walls of the stomach, especially its 

 upper part, and partly into the bases of the tentacles and the parts 

 immediately around the mouth. Below the stomach each retractor 

 muscle (Figs. 10 and l-ip) does not extend over the whole width of the 

 septum, but is confined to its outer half. 



The transverse sections drawn in Figs. 13 and 14 show some 

 further points of importance concerning these muscles. They show, 

 firstly, that the retractor muscles, which lie between the mesoderm (x) 

 and endoderm {>j) do not lie on both sides of the septa, but only on 

 one side of each. A more important point, shown clearly in the 

 figures referred to, is that the muscles do not lie on the same side of 

 all the septa. Thus, on the left hand side of Figs. 13 and 14, is a 

 compartment of the body-cavitj-, bounded by two mesenteries in 

 which the retractor muscles face away from one another ; while on 

 the right hand side of the figures is one in which the retractor 

 muscles face towards one another. In the intermediate septa, whether 

 above or below the stomach in the figures, the retractor muscles are all 

 on the right hand side of the septa. 



Owing to tliis arrangement it is seen at once that there is only one 

 possible bisecting plane that will divide the polype longitudinally into 

 two perfectly symmetrical halves, i.e., a plane passin ~[ through the 

 middle of both the right hand and the left hand com]uirtments ; or in 

 Plate II., a plane indicated by a horizontal line drawn across the 

 middle of the figures in qiteslion. 



This plane of synimetri/, as is shown in Figs. 12 and 13, is also 

 the one which passes through the long axis of both the mouth and the 

 opening from the stomach to the body-cavity, and is the plane of 

 bisection adopted in Fig. 10. 



A less important point, shown by the sections in Figs. 13 and 14, is 

 that the longitudinal muscles extend a short distance round the body- 

 wall on either side of the lines of attachment of the septa, forming, 

 by so doing, the system of longitudinal muscles of the body-wall 

 referred to on a preceding page. 



Besides the large retractor muscles there is in the upper part of 

 the polype a second much weaker set of muscles crossing the former 

 at right angles, and having an antagonistic action. These protractor 

 muscles (Fig. 10 q) arise from the upper part of the body-wall, and 

 from the calyx, run downwards and inwards in the septa, and are 

 inserted into the mesoderm of the stomach wall. Their action is to 

 pull up the stomach after it has been drawn down by the retractors. 



