528 OLWEN M. REES. 



In the mesenteries (Fig. 4) of the first two cycles the parieto-basilar 

 is comparatively strong ; it is slightly constricted near the base, and is 

 an elongated muscle. Most of the muscle folds are given ofi on one side 

 only. These folds are short and stout, sometimes globular at the head, 

 sometimes slightly branched. Before the parieto-basilar muscle passes 

 into the retractor muscle the former becomes swollen and a projection of 

 the mesogloea sends out a number of branches towards the edge away 

 from the retractor muscle. 



The longitudinal retractor muscle is rectangular in section and has an 

 appearance quite different from that of S. miniata. In the latter the 

 muscle folds are delicate and very numerous — about 80 in number ; 

 while in S. ornata the folds are fairly short and stout and number only 

 about 10-20. 



Oral stomatopores are present in the complete mesenteries, and there 

 are slits between the retractor and parieto-basilar muscles. 



The mesenteries of the third cycle reach about half-way across the 

 coelenteron. Each mesentery has a stout axis of mesogloea, which gives 

 off about five branches. 



The mesenteries of the 4th cycle are present in the lower half of the 

 column only. They are very small and are indicated by a thin pro- 

 jection of mesogloea surrounded by a layer of endoderm. 



Stomatodaeum. The two oesophageal grooves are well marked. The 

 ectoderm is thick and has a granular zone near the free surface. The 

 mesogloea is thick near the base of the groove, but becomes thinner along 

 the sides of the groove. The wall of the stomatodaeum is raised into about 

 24 deep folds, corresponding to the number and attachment of the 

 mesenteries, and the ectoderm of these folds contain a large number of 

 gland cells whose contents are not granular. 



The sphincter muscle (Fig. 5) is a mesogloeal one. It is very much like 

 that of *S. mihnani (H. and S.) figured by Haddon in Trans. R.D.S., 1898. 

 The cavities in the muscle are large and numerous and tend to radiate 

 in the same direction as shown in the figure. The broadest region is near 

 the summit, w^hile lower down in the column wall the muscle becomes 

 very narrow and the cavities become fewer. The gland cells of the 

 ectoderm in this region contain a number of spherical bodies which are 

 highly refractive. 



Tentacles. Near the tip the ectoderm is more than twice as thick as 

 the rest of the tissue. In a section through this region of a tentacle there 

 are very numerous nematocysts, some seen in section and some seen 

 from the side. They are fairly short and stout, spindle-shaped bodies, 



