ACTINIARIA 



207 



order should be situated, if the}' were developed as in Actinostola spetsbergensis. In this species the weakest 

 mesenteries of the third cycle are found next to the mesenteries of the first cycle, the stronger mesenteries 

 next to the mesenteries of the second order. In Pycnanthus densus we see that in the first compartments, 

 next to the one directive pair, the mesenteries of the fifth cycle are lacking between the directive pair and that 

 of the third order, while such mesenteries are developed between the pair of the third cj'cle and that of the 

 second. In the other primar\' compartments there are mesenteries of the fifth order, except on one side 

 where they are lacking in four exocoels, placed between the mesenteries of the tliird and first orders. In eight 

 exocoels, four on each side, mesenteries of a sixth cycle are present. If these latter were established in strict 

 conformity with the rule of Actinostola, they should appear between the mesenteries of the fourth and second 

 cycles. They have, however, here arisen between those of the third and fourth cycles, which seems to be 

 connected with the fact (in contradistinction to the Actinostola) that the weakest mesentery of the fourth 

 cycle (in the scheme marked with a *) stands next to the pair of the second cycle, not as in Actinostola next 

 to that of the third. The with a * marked pair of the fourth order namely shows a different development of 

 both mesenteries in the same pair, one being perfect, the other not. 



The mesenteries of the second specimen were 216 in number. The arrangement of the 108 pairs 

 agrees well with the agroupment of the mesenteries in spec. i. The mesenteries of the sixth cycle namely 

 have arisen in the same secondary compartments (between the mesenteries of the first and second orders) 

 as in spec, i viz. counted from the one directive pair in the secondary compartments 3 and 5, on each side 

 of the directive plane (compare the arrangement in spec. i). The number of mesenteries was, however, in 

 two such compartments a Httle more numerous here than in spec, i, namely 11 pairs in compartment 5 on 

 one side, and in compartment 3 on the other, instead of 9 in the two other compartments and in the corres- 

 ponding compartments of spec. i. In the other secondarj' exocoels there were mesenteries of the third to the 

 fifth cycles, regularly arranged. Whether a difference in size exists between both mesenteries of the same pair 

 in the mesenteries of the fourth cycle I cannot decide, as I did not want to cut up the specimen. For the 

 same reason I have not examined the number of the perfect mesenteries here. 



The mesenteries of the three first cycles were perfect in specimen i. Two unpaired mesenteries of the 

 fourth cycle besides reach the actinopharjmx, as above mentioned. In a couple of cases I have observed a slightly 

 different size of both mesenteries of the third cycle, the weakest mesenter\' in the pairs is next to the mesen- 

 teries of the first order. Though the arrangement of the mesenteries does not quite agree with that of the 

 Actinostolids, it, however, seems to recall the latter. 



The mesenteries were provided with comparatively small oral, but with large marginal stomata. 

 Their mesogloea is rather thick. The longitudinal muscles form no distinct pennons and show, on transverse 

 sections, rather coarse folds, scattered over the whole surface. The parietobasilar muscles are distinctly outlined 

 and reach the region of the marginal stomata. Through the growth of the parietobasilar muscles one part of 

 these muscles becomes mesogloeal as in Stomphia. The reproductive organs of specimen i are found on the third, 

 on the greater part (18 pairs) of the fourth, and on four pairs of the fifth cycle. In the scheme I have marked 

 the fertile pairs with spaced out figures. The younger sterile pairs, 6 of the fourth order, 32 of the fifth and 

 8 of the sixth, are very weak , appear only in the most proximal part of the body, and are devoid of fila- 



