246 PROFESSOR OSKAR CARLGREN ON THE GENUS PORPONIA 



The filaments are well developed and extremely broad, owing to the strong develop- 

 ment of the mesogloea (Plate, fig. 9). The vacuolar streak is little differentiated. Both 

 in the intermediate part of the ciliated tract region and in the nematocyst glandular 

 streak there are sparse spirocysts and fairly numerous thick-walled nematocysts, 

 especially in the latter (length 36-41, sometimes even 46 M, and about 3 M broad). Of 

 fairly common occurrence further in the glandular streak are nematocysts with distinct 

 basal part to the spiral thread (length 37-41 /u, breadth 7 M). Even the entoderm of 

 the filament is pigmented, especially on the region of the border-streak. 



The sexual organs occur on all well-developed mesenteries, even on the directive 

 mesenteries. The animals are dioecious. 



For the Porponia obtained by the Scotia Expedition I have set up a new species, 

 P. antarctica. Of the species of Porponia already known it comes nearest to 

 P. robusta, R. Hertwig, both in the form of the body and the appearance of the 

 tentacles. To set up good characters between these two species is, however, distinctly 

 difficult, as HERTWIG'S description of P. robusta is so incomplete, and both, this species 

 as well as the two specimens of P. elongata, do not seem to have the number of 

 mesenteries and tentacles typical of P. antarctica. It is probable that the mesenteries 

 of the fifth order have not been laid down in HERTWIG'S form, to judge from the 

 number of tentacles, which HERTWIG gives to be 54 in P. elongata. According to 

 some notes made by me in 1897 on revising the Challenger Actiniae, the distribution and 

 size of the spirocysts and nematocysts in P. robusta and P. elongata were as follows : 



The spirocysts in the body-wall were in P. robusta very numerous and about 

 40-44 M long, in the tentacles of P. elongata about 56-72 /* ; there were also spirocysts 

 in the ossophagus of these two species. The nematocysts in the oesophagus were 48 M 

 long in both P. elongata and P. robusta, in the tentacles of P. elongata 48 M long. 

 It is, however, noticeable that there were only fragments of the ectoderm in the 

 Challenger species. 



II. ON THE SYSTEMATIC POSITION OF THE GENUS PORPONIA. 



According to the anatomical account of the genus Porponia given above, there 

 should be no doubt remaining that Porponia and Halcurias (Endoccelactis} are very 

 nearly related to each other. Common to both is the structure of the body-wall, and 

 also of the oesophagus, both, among other things, being provided with numerous spiro- 

 cysts. Even the anatomical structure of the filaments and distribution of the sexual 

 organs show agreement. Most striking, however, is the characteristic and similar 

 arrangement of the tentacles and mesenteries, which differs from that in all other 

 known Actiniaria, as can be seen more clearly from the following scheme for the two 

 genera. In both Halcurias and Porponia the same displacement of the original 

 mesenteries and tentacles has clearly taken place. After the formation of the first 6 pairs 

 of mesenteries, 1, 1, etc., in the ordinary way, 2 mesenteries (2, 2), with the longitudinal 

 muscles faced outwards, have arisen in the lateral endoccels, and these mesenteries 



(ROY. soc. EDIN. TRANS., VOL. L., 54.) 



