130 



ACTINIARIA 



The a-nematocysts of the column were generally more thin in the distal end, in the specimens i and 

 3 sometimes a little curved and with indistinctly visible basal part to the spiral thread. In the specimen 2, 

 the maceration preparations of which are a little unreliable in consequence of the bad state of preservation, 

 the basal part of the spiral thread was visible, most of the capsules were destroyed here and only the rib-like 

 basal part left. The b-capsules of the column were of equal breadth. In the a-capsules of the actinopharynx 

 the basal part of the spiral thread was more or less visible, the a-capsules were broader in the basal end, 

 the b- and c-capsules were in all places equally broad. The main part of the capsules in the tolumn and the 

 actinopharynx consists of a-capsules, the b- and c-capsules were very sparse. The nematocysts of the ten- 

 tacles were rather sparse, the spirocysts numerous. The a-capsules of the actinopharynx vary a little in size, 

 I must, however, mention that the size of the capsules in the actinopharynx is unreliable, according to the 



strong compression of this part ; it is possible that 

 one part of the capsules belongs to the filaments. 

 The size of the nematocysts and the spirocysts 

 besides agrees well in the four specimens. 



The mesogloea of the column is not thick but 

 very fibrillated, the endoderm is thin. The endo- 

 dermal circular muscles are not strong, in the re- 

 gion of the fossa a little stronger, but form no dif- 

 ferentiated sphincter (four specimens examined 

 in this respect). The longitudinal muscles of the 

 tentacles and the radial muscles of the oral disc 

 are well developed. 



The pairs of mesenteries are arranged in three 

 cycles 6 -f- 6 + 12 = 24. In addition to these pairs 

 a fourth cycle is probably present in the largest 

 specimen reproduced in fig. 31, PI. i. This spec- 

 imen was namely provided with a greater number 



Textfigs. 153 — 154. Haliaclis arctica. 

 Fig. 153: Transverse section of a perfect mesentery in the repro- of tentacles than the other specimens (compare 



ductive tract (spec, from Greenland, .iiyanihus.). Fig. 154: Trans- above) . Only the mesenteries of the first CNxle are 



verse section of mesenteries of the second and third order and of 



Fig 154- 



an acontium (ac) (spec, from Bear Isl.^ 



perfect and strongly developed, the other mesen- 



