214 



ACTINIARIA 



Textfigs. 200 201. 



Sicyonis tuberculata. 

 Transverse section of 

 tentacle near its base 

 (fig. 200) and of the 

 middle part of the 



sphincter (fig. 201). 



section of sphincter in its middle part). The ectoderm of the tentacles is on the base of the outside low, on 

 the inside a little thicker, more upwards the ectoderm of the outside is also thicker. It contains rather numer- 

 ous to numerous nematocysts, 19 34x2,5 p large, and very numerous spirocysts of variable length, from 

 22 X 2 to 55 x 5 fji (3 specimens examined). The tentacles are devoid of longitudinal muscles on the abaxial 

 side at the base, more upwards there are solitary muscle-meshes in the mesogloea (textfig. 200, transverse 

 section of tentacle near its base) , and in the distal part, above the swelling of the mesogloea, numerous meshes 

 of the same size as those at the adaxial size, where the muscle-meshes are numerous also at the base. The 



muscle meshes are more or less delicate and often elongated in radial 

 direction. The mesogloea is considerably thicker than the ectoderm, 

 excepting at the apex of the tentacles. The radial muscles of the 

 oral disc recall the outer tentacle-lacking parts of the longitudinal 

 muscles of the tentacles and form thin meshes, elongated in the di- 

 rection from the ectoderm to the endoderm. At the insertions of the 

 mesenteries they are interrupted by thicker mesogloeal balks. In the 

 vicinity of the actinopharynx the muscle meshes are small and few. 

 The ectoderm of the actinopharynx is rather high, strongly pig- 

 mentous and contains numerous, typical nematocysts, 24 31 X 2,5 // 

 in size, and rather numerous nematocysts with discernible basal 

 part to the spiral thread (size 24 29x5 p. 3 specimens examined). 

 The arrangement of the mesenteries is rather peculiar and 

 shows a tendency to an octomerous development, in as much as often 

 16 pairs are perfect; there are besides some fewer or more numerous 

 pairs, of which one mesentery is perfect, the other not. We also often 

 may find several imperfect pairs of mesenteries of which one mesen- 

 tery is more strongly developed than its partner. I have, however, 

 not made any observations, definitely proving the mesenteries to be 

 arranged, according to the same distinct law as in the Actinostolids, 

 though the mesenteries on both sides of the directive plane are 

 often symmetrically grouped. Five examined specimens show the following arrangement of the stronger 

 mesenteries. Issuing from one directive mesentery we follow the mesenteries as the figures on a dial and, if 

 necessary, call the mesentery next to the directive mesentery a, its partner b. (The reproductive mesen- 

 teries are not enumerated in the scheme). 



The following pairs of mesenteries were perfect in: 

 Sp. i (St. 32) 



3, 6, 7, 9, 12, 13, 15, 17, 19, 21, 22, 25, 27, 28, 31 = 16 pairs (textfig. 2025). 





Fig. 200 



Fig. 20L 



Sp. 2 (St. II) 

 Sp. 3 (St. II) 



Sp. 4 (St. ii) 

 Sp. 5 (St. 32) 



i, 3. 6, 7, 9, 12, 14, 16, 18, 20, 22, 24, 27, 29, 30, 33 = = 16 pairs (textfig. 202,4). 

 i, 3, 6, 7, 9, 12, 13, 15, 17, 19, 21, 22, 26, 28, 32 = 15 pairs (textfig. 202 C). 



