232 



ACTlNIARlA 



The mesenteries are hexaraerously arranged in 5 or 6 cycles. The mesenteries of the three first orders 

 are perfect, though those of the third order do not reach as far down on the actinopharynx as both the first. 

 Both mesenteries in the pairs of the third cycle seem to be about equally developed. From the mesenteries 

 of the fourth cycle the mesenteries are distinctly arranged, according to the Actinostola-rule. The 12 first pairs of 

 mesenteries are sterile like those of the youngest cycle, sometimes also one part of the last cycle but one. 

 The species is monoecious, and testes and ovaries were simultaneously developed. As far as I have observed, 

 the mesenteries of the third cycle always have ovaries, those of the fourth cycle now ovaries, now testes, 

 sometimes both mesenteries of this cycle are only provided with testes, sometimes the strongest mesentery 

 of a pair has ovaries, the weakest testes. The mesenteries of the fifth cycle as a rule form testes. I have, how- 

 ever, found specimens, in which testes are present only in a part of the mesenteries, while the others have 



ovaries. The testes, when found, were always numerous. 

 Rather often testes and ovaries may be found in the 

 same mesentery. There is thus a great variation in the 

 distribution of the testes and the ovaries, still it seems, 

 as if the ovaries appear on the older, the testes rather 

 on the youiiger mesenteries. In the textfig. 209 I have 

 reproduced a transversal section of a part of a mesen- 

 tery with ovaries (ov) and testes (t) . The ovaries, as well 

 as the testes were well developed ; in a specimen, one of 

 the largest of the collection, the reproductive organs 

 were absent. 



The longitudinal muscles of the mesenteries form 

 no pennons but are ordinarily developed, the transversal 

 muscles are distinct and the parietobasilar muscles 

 strong, well marked and almost reach the sphincter. 

 The basilar muscles on transverse sections are of about the same appearance as in A. spetsbergensis, though 

 the muscle lamella are more extended along the sides of the mesenteries than in this species. I have not 

 observed any marginal stomata; on the other hand, there are commonly oral stomata. I have found small 

 young in the coelenteric cavity of two specimens, in the one specimen they were very numerous. In this 

 respect the species agrees with A. spetsbergensis. 



Genus Stomphia Gosse. 



Diagnosis: Paractiidae (Actinostolinae) with well developed basal disc and rather thin to thick, 

 in contracted state rugose body-wall, which is devoid of tubercles, verrucae, acrorhagi, and fossa. Sphincter 

 strong, so that the body-wall may cover the tentacles. Tentacles short, conical, in. contracted state wrinkled 

 or longitudinally sulcated, always without thickenings on the outer side, and like the mesenteries arranged 

 after the number 6 + 10 (12) + 16 (18). Inner tentacles longer than outer. Longitudinal muscles of the 

 tentacles and radial muscles of the oral disc mesogloeal. Actinopharynx of ordinary length with two well 



Textfig. 209. Actinostola groenlandica. 



Transverse section of part of a mesentery with ovaries 



and testes. 



