20 



ZOANTHARIA 



that in the furrows of the capitular region it is only separated from the ectoderm by a very small 

 part of the mesogloea, which in this region is generally higher than in the other parts of the body 

 and contains some nematocysts. 



The tentacles have the usual structure. Besides the very numerous spirocysts the ectoderm 

 contains numerous, thick-walled capsules (length 14 — 17 /y>) and a few capsules of the same appearance 

 as in the body-wall (length 24 — 26 /i, breadth 10 ft). 



The ectoderm of the oral disc is very broad near the tentacles and contains numerous, closely 

 packed spirocysts, near the mouth it is thinner and contains some nematocysts. The ectodermal 

 longitudinal muscle layer is fairly strong in the outer part of the oral disc, weaker in the inner part. 

 A layer of fibrillae and ganglion cells is distinctly visible in the oral disc. 



The ectoderm of the oesophagus is high and arranged in longitudinal folds supported by 

 mesoglceal ridges, which emerge between the furrows. The nematocysts are scarce and thick-walled 

 (length about 20 u). Large-grained gland-cells are found especially in the inner parts of the ectoderm. 

 Ectodermal longitudinal musculature is absent in this species. At the base of the ectoderm of the 

 oral rim there seem to be numerous cells and a thread-like layer. As far as I can see — the 

 material was not so well preserved as could be desired — it consisted of a well-developed layer of 



ganglion-cells and nerve-fibrillae. The mesogloea is fairly 

 thick; its upper part is provided with numerous cells which 

 are scarce in the aboral part. The ectoderm of the siphono- 

 glyphe is of the usual structure and lower than in the other 

 part of the oesophagus. The mesogloea is broad and much 

 thicker than in the oesophagus. The hyposulcus has the 

 same structure as the siphonoglyphe but the entodermal 

 muscles here run in longitudinal direction and form some 

 folds in the outer parts. The free border is thick and 

 even provided with more numerous gland-cells than the 

 inner parts. 



The number of mesenteries varies according to 

 the size of the polyp. In a smaller specimen 24 meseu- 



Text fig. 4. Transverse section through a piece of the teries were developed. 14 macro and 10 micro. Two 

 body-wall with mesenteries and oesophagus of Epi- larg . e po i yps had 46 mesenteries. They were both ir- 



zoanthus norvegicus. Ectoderm shaded, mesogloea 



and muscles black, entoderm not specially marked, regularly developed, the one side having more mesen- 

 dc: directive chamber. teries than ^ Qther Qne q{ ^ polypg j^ ^ m ^ Q 



and 11 micromesenteries on the one side of the sagittal plane, and 12 macro and 10 micromesen teries 

 on the other. The other polyp had 11 macro and 9 micro mesenteries respectively and 14 macro and 

 12 micro. The micromesenteries are strong. The longitudinal musculature of the mesenteries is 

 vigorous and forms fairly numerous folds. The parieto-basilar muscles are weak. The distribution of 

 the longitudinal and the parieto-basilar muscles on the body-wall is slight. The muscles of the 

 micromesenteries are generally well-developed (text-fig. 4). 



The filaments have the usual characteristic structure. The glandular tract contains only the 



