

ACT1NIARIA 



There are 10 pairs of mesenteries, two of which are directives; the ventral pair is connected with 

 the siphonoglyphe ; all mesenteries are perfect and fertile. The longitudinal pennons (fig. 143) are very strong 

 and in the reproductive region provided with about 30 lu'gh, dichotomously branched folds, most of which 

 are of about equal height; the inner and the outer parts of the pennons are almost equally developed. The 

 parietal muscles (fig. 143) are well differentiated, in their inner part either transversally expanded or in the 

 lower part of the reproductive region more thin but longer. The outer part of the parietal muscles is weak 

 and not expanded upon the body-wall. The part of the parietal muscles corresponding to the parieto-basilar 

 muscles is sharply indicated, and a deep fold separates it from the mesogloeal main lamella of the mesen- 

 teries. Sometimes the mesogloea of both sides of this fold is coalesced, so as to form meshes in transverse- 

 sections, a structure recalling that of the parieto-basilar muscles of for instance Stomphia. The ciliated streaks 

 are also found on the ventral directives what is not the case in Peachia. The median streak of the filaments 

 are provided with numerous, small, rib-like nematocysts, about 14 17 X 2 // in size; large nematocysts 

 are very sparse. In the cnido-glandular tract, on the other hand, large nematocysts are more common ; they 

 are partly 58 67 X 6 fi, partly 68 79 X 4 // in size. Besides these, there are small nematocysts as in the 

 median streak. The intermediate streak is well differentiated and provided with numerous gland-cells. The 

 mesogloea of the filaments contains sparse cells. There is a very large marginal stoma in each mesentery. 

 The oral stoma is rather large. The specimen is dioecious. 



Description of a young specimen: The specimen, dredged in Hjalte fiord, was not sexually 

 ripe and differs in some points from the adult specimens. Its length was 1,5 cm, the largest breadth 0,25 cm, 

 and the length of the tentacles about 0,2 cm. The exterior of this specimen is shown on the figure i, PI. i. 

 The physa was ampullaceous, the elevations of the column distinct, especially in the distal part. The visible 

 tentacles were n ; as there are 12 mesenteries it is probable that one more tentacle is present, though involved ; 

 I cannot, however, decide it as I have not sectioned the distal part. The aboral prolongation of the siphono- 

 glyphe was rather well developed. 



In order to make an anatomical examination of this specimen I have cut out a piece about 0,6 cm 

 long, encluding the lower part of the region of the actinopharynx and a part below this region. The text- 

 figure 142 shows a transverse-section through the lower part of the region of the actinopharynx. The sipho- 

 noglyphe is, seemingly, well developed, the albumen-cells are rather numerous, the endoderm of the sipho- 

 noglyphe is high, and, in contradistinction to the other endoderm of the actinopharynx, it is of a bladdery 

 structure. The elevations of the column were not as distinctly differentiated as in the sexually mature spec- 

 imens. The perfect mesenteries were 12 in number, namely 6 pairs. In a lateral exocoel one pair of weak 

 imperfect mesenteries rose slightly over the surface of the column ectoderm. The lateral mesenteries of the 

 second order thus arise earlier than the ventro-lateral mesenteries, in other words, the development of the 

 mesenteries of the second order proceeds in a dorso-ventral direction, though the dorso-lateral mesenteries 

 are suppressed. The fifth and the sixth couples of mesenteries arise as in Halcampa, the ventro-lateral couple 

 thus being the weaker. None of these couples reach the undermost part of the actinopharynx. The longi- 

 tudinal pennons are weaker than in the sexually ripe specimens. The folds are only slightly branched, in 

 the lower part of the actinopharynx they are about 10 in number, below the actinopharynx a little more 



