Miss O. M. Roes on Actinostola callosa. 



385 



mesenteries of the fourth cycle. The mesenteries are there- 

 fore arranged in five cycles, thus: — 6 -f (>+ 12 + 24 + 48. 



The musculature of the mesenteries is not very strongly 

 developed. There is a fairly distinct parieto-basilar muscle, 

 which, on its distal end, is continued into a slender elongated 

 longitudinal muscle. The muscle-folds are not numerous. 

 They are slender, swollen at the tips, and sometimes divided. 

 'The ectoderm of the column-wall is thick, and contains 

 numerous large yellowish gland-cells. The mesogloea is 



Fiff, 3. 



Portion of a transverse section through the oral disc, showing 

 two layers of muscles. 



Index to lettering. 



d., directive mesenteries. 

 ec, ectoderm. 

 en., endoderm. 

 oes.gr., oesophageal groove. 



ec.M., ectoderm lining the stoma tod-emu. 

 mes.fil., mesenteric filament. 

 ff.c, gland-cells. 

 m.\, upper layer of muscle. 

 m. 2 , lower layer of muscle. 



»., nematocysts. 

 n.l., nerve-layer. 



strong, becoming fibrous towards the inner surface. On 

 its outer surface it is raised into lobes, and these are covered 

 with ectoderm. These account for the wrinkled appearance 

 of the exterior of the animal. The ectoderm lining the 

 stomatodamm is much folded, and its cells form a spongy 

 mass. The mesogloea is dense and thin, sending out pointed 

 projections into the ectoderm. The mesogloea of the tentacles 

 is also very thin and, in longitudinal sections, is seen as a 

 uniform layer reaching the base of the tentacle without giving 

 Ann. & M(uj. N. Hist. Ser. 8. Vol. xii. 28 



