ACTINIARIA jj- 



whether a pair of mesenteries belongs to an older or a younger cycle, because all pairs of mesenteries and 

 often also both mesenteries of one pair are differently developed, as regards the muscle-pennons. The lon- 

 gitudinal muscles of the pennons are strong, in transverse-sections elongated with numerous (about loo) 

 close folds, almost all of about equal height, whereby the pennons in transverse-sections get a comb-like 

 appearance. The main lamella of the mesogloea is tliickened in the outer part of the pennons, in the inner 

 part thin. The outer, more lamellar part of the mesenteries is attached to the outside of the pennons. The 

 inner part of the pennons is on the directive mesenteries curving towards the endocoels, on the other mesen- 

 teries towards the exocoels (textfigure 144. Transverse-section through a mesentery in the reproductive 

 region). The parietal muscles are comparatively weak, with rather low folds, smooth or a little ramificated, 

 especially on the side of the pennons. On the opposite side they are, however, more high and a little more 

 richly branched (Fig. 145. Transverse-section of the outer part of a mesentery). The}- are not expanded on 

 the column. No basilar muscles present. As far as I can see the oral stomata are also lacking. A large stoma, 

 probably a marginal stoma, is visible on the mesenteries, aside from the pennons, rather near the upper 

 end. The mesenterial filaments are very long and extended almost to the proximal end of the animal. The 

 ciliated streaks are well developed. The mesogloea of the filaments is thick and contains few cells, poor in 

 protoplasm. Inside the parietal muscles the mesogloea is very much thickened. 



Family Halcainpidac. 



Diagnosis: Athenaria with commonly elongated, cylindrical body, with a simple or double meso- 

 gloeal sphincter, without acontia. Column divided or not divided in regions. Perfect mesenteries 8 to 12 

 (or more?). Ciliated streaks present, sometimes discontinuous. 



Concerning the arrangement of this family, its designation and the genera, which, according to nie, 

 belong to it, compare p. 19, 21, 22. 



The type of the genus Halcampa, after which the family is named, has, as I suggested (1893, p. 37), 

 and as I have shown (1900 b, p. 11 71), a mesogloeal sphincter, which Stephenson (1918, p. 9) has at length 

 confirmed. 



Genus Halcampa Gosse. 



Diagnosis: Halcampidae with the column divisible into three regions, physa, scapus and capi- 

 tulum. Physa ampullaceous with pores in one or two cycles. Scapus with papillae ("Ha/cam^a-papillae") 

 to which grains of sand often adhere. Ectoderm of the capitulum with numerous spirocysts, with a well 

 developed layer of nerve-cells and nerve-fibrillae, in the uppermost part with longitudinal muscles forming 

 a prolongation of the muscles of the tentacles and of the oral disc, and probably belonging to these muscles. 

 Sphincter comparatively weak, often close to the ectoderm and expanding a httle into the base of the ten- 

 tacles. Tentacles 8 to 12, short, of equal width, with rounded apices. 2 rather sUght siphonoglyphes and 2 

 pairs of directive mesenteries. 8—12 perfect and 6—12 fertile mesenteries forming strong pennons, besides 

 a more or less perfect second cycle of very weak, sterile mesenteries, never producing pennons, but expanded 

 over almost the whole length of the column. 



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