ACTINIARIA 



203 



Fig. 19 



Fi<»- 194 



number of tentacles is about 96 (6 + 6 + 11 + 24 + 48), the inner are many times larger than the outer. 

 Sometimes the tentacles are indistinctly longitudinally sulcated. The oral disc is wide, its larger part has 

 no tentacles. It is provided with indistinct radial furrows, corresponding to the insertions of the mesenteries. 

 Actinopharynx is of ordinary length, irregularly wrinkled and provided with 2 deep siphonoglyphes. 



Anatomical description: The ectoderm of the col- 

 umn is almost lost, only a few fragments of it were present in 

 several invaginations. In these fragments I found nematocysts, 

 14 — 17 X about I fi in size. Its mesogloea is thick and shows 

 the same differentiation into two layers, an outer, provided 

 with numerous cells and an inner, fibrillar and poor in cells, as 

 that which I have described more in details for Sicyonis 

 tuberculata. The endodermal circular muscles are weak, the 

 distinctly longitudinally stratified sphincter, however, strong. 

 In the uppermost part it occupies almost the whole breadth of 

 the mesogloea, diminishes rapidly and passes into the endodermal 

 circular muscles (textfig. 192, 193). The ectoderm of the ten- 

 tacles is high with very numerous spirocysts (size : from 17x1 n 

 to about 41 X 4,5 fi) and also rib-like typical nematocysts (size 

 22 X 2 — 31 X 2,5 //). Besides these, there are sparse nematocysts 

 with discernible basal part to the spiral thread (size about 31 — 

 36 X 3 — 3,5/^). The mesogloea of the tentacles is thinner than 

 the ectoderm. The longitudinal muscles form numerous, closely 

 packed, radially extended meshes in the mesogloea. On the outside 

 of the outermost tentacles, lowermost at the base where the me- 

 sogloea is a little thickened, the longitudinal muscles are lacking, 

 the muscle-lacking part, however, being inconsiderable (textfig. 

 194). Not far from the base, scattered muscle fibres namely ap- 

 pear, rapidly increasing in number. The larger part of the outer 

 tentacles displays uniformly extended muscles. The mesogloeal 

 radial muscles of the oral disc are in the inner part of the disc 

 weak and commonly only separated from the ectoderm by a thin lamella, in the outer parts strong with 

 closely packed meshes, extended in ecto-endodermal direction. At the insertions of the mesenteries the mus- 

 cles are interrupted by mesogloeal bridges. The ectoderm of the actinopharynx is of ordinary height and 

 contains numerous nematocysts, 25 X 2 to 31 X 2,5 [i in size. Its mesogloea is thicker than its ectoderm, 

 especially in the siphonogh'phes. Concerning the structure, the mesogloea of the actinopharynx agrees with 

 that of the inner part of the column, in the siphonoglyphes and in the vicinity of these latter the meso- 

 gloea is not so strongly fibrillar; here as in the Zoantharia there are also scattered ceU-islets. 



The number of the pairs of mesenteries is 96 or thereabout. The mesenteries are arranged in five 



26» 





f- 





^^^ 



I 





<33o 



Fig. 193 

 Textfigs. 192 — 194. Pycnanthus laevis. 

 Fig. 192: Transverse section of sphincter. Fig. 193: 

 Transverse section of part of the sphincter (in the 

 fig. 192: indicated by dotted lines). Fig. 194: Trans- 

 verse section of an outermost tentacle, next to 

 its basis. 



