206 ACTINIARIA 



very numerous nematocysts and spirocysts. The size of the former is in spec, i 36 — 48 x 2,5 — 3 /i (commonly 

 they are 41 — 43 ft long), in spec. 2 34 — 41 X 3 — 2,5 fi, the latter variates in spec, i from 24 X 1,5 /u to 58 X 

 3,5 n, in spec. 2 from 22 X 2 to 48 X 4,5 /x. The mesogloea of the tentacles is thicker than their ectoderm, 

 the longitudinal muscles are found in the middle part of the mesogloea and show rather large meshes on trans- 

 verse sections. The radial muscles of the oral disc (textfigs. 196, 197) are also mesogloeal, but approached 

 to the ectoderm and in the outer part of the disc separated from it only by a thin layer of mesogloea (textfig. 

 196). The muscles seem to be continuous and not interrupted at the insertions of the mesenteries, the meshes 

 of the muscles are rather large, Uke those of the tentacles. The mesogloea of the oral disc shows in the parts, 

 which are not occupied by the muscles, a chondroid-shaped structure. Tlie ectoderm of the actinopharynx 

 contains typical nematocysts, the size of which is in spec, i 29 — 36 ^ long and 2,5 // broad (a few nematocysts 

 reach a size of 29 x 3,5 fi), in the spec. 2 24 — 31 X 2 — 2,5 //. Besides these, there are here numerous nema- 

 tocysts with distinct basal part to the spiral thread, in spec, i 20 — 24 X 3 — 3,5 /i, in spec. 2 22 — 29 X 3,5 — 5 fi. 

 In the maceration preparation I have found also spirocysts here, which, however, probably do not belong to 

 the actinopharynx, but are attached to the ectoderm. 



The number of the pairs of mesenteries was in spec, i probably 92. On one side of the animal, 

 counting from one directive to the other, I observed 48 pairs, on the other side I examined only the larger pairs, 

 being 22 in number. As there are pairs, alternating with these latter, of wliich I have convinced myself by the 

 examination of some compartments , the number of the pairs of mesenteries is on this side probably 44. If 

 we indicate the different cycles by letters — the mesenteries of the first order by Roman figures — the 

 arrangement of the pairs of mesenteries is as follows, {dm : directive mesenteries. Concerning the spaced out 

 figures compare below!). 



On one side : 



dm. # 



143545254534 154536564525453545 154536564525453545 = 48 pairs. 



on the other side: 



« dm. 



43545254534 154536564525453-4- I 54536564525453-4-1 = 44pairs. 



As we see, the arrangement of the mesenteries is almost the same on both sides. The only difference 

 is that 4 pairs of mesenteries of the fifth order are not developed on one side (in the lower line). On closer 

 examination of the arrangement, it appears that it is irregular. In the primary exocoels, on both sides of one 

 directive, we observe mesenteries of the second to the fifth orders, those of the fifth order are, however, de\'el- 

 oped only between the mesenteries of the third and second cycles, but not between those of the third and 

 first. In the 4 other primary exocoels the mesenteries are numerous and show the same agroupment in all 4, 

 excepting that 4 pairs of mesenteries are lacking on one side. In all these primary exocoels, mesenteries of the 

 second to the sixth cycles are developed, those of the sixth cycle are, however, limited to eight pairs, two 

 in each primary exocoel, on both sides of a pair of the fifth order. Comparing this arrangement with that of 

 the ActinostoUds we find a certain agreement. It is true, that both mesenteries of the same pair in the younger 

 cycles of Pycnanthus densus generally are of the same size, but the failure or the retardation in the erection 

 of the youngest cycles takes place in the compartments on the side, where the weakest mesenteries of the third 



