296 Soittheru Cross. 



Tentacles. — These are forty-eight in number, in four cycles, 

 (3 _|. 6 + 12 + 24. Fig. 8 diagrammatically represents the arrange- 

 ment of the cycles of tentacles in relation to the inter- and intra- 

 mesenteric spaces. It will be seen the older and inner three cycles 

 (6 4- 6 -f- 12) open from the intra-mesenteric spaces, while the outer 

 maroinal and youngest cycle opens from the inter-mesenteric spaces. 

 In most cases there is a distinct longitudinal grooving, and transverse 

 sections of the tentacles show in w^ell-marked instances that the meso- 

 gloea participates in the formation of the grooves (fig. 3), although 

 this is not always the case. The muscles of the tentacles are ecto- 

 dermal and are well developed. 



CEsophagus. — This extends fully three-fourths the length of the 

 retracted column. Two well-marked siphonoglyphs are present at 

 opposite angles. 



Cceknteron and Mesenteries. — There are twenty-four pairs of 

 mesenteries in three cycles, 6 -f- 6 + 12, all complete. There is no 

 trace even in the largest specimens of a fourth cycle. The presence 

 of a cycle of tentacles communicating with the inter-mesenteric 

 spaces suggests the final and adult condition of mesenteries and 

 tentacles. 



Two pairs of directive mesenteries are present in the usual 

 relation with the siphonoglyphs. All the mesenteries except the 

 directives are fertile. 



One variation from the typical arrangement of tentacles and 

 mesenteries was dissected. The specimen, which possesses brood 

 chambers containing embryos, had but eighteen pairs of mesenteries 

 and thirty- six tentacles, and the two pairs of directives were 

 asymmetrically placed, being separated from one another on the one 

 side by ten pairs and on the other by six pairs of mesenteries. 



The longitudinal muscles of the mesenteries are very well deve- 

 loped, and form large swellings which stand out prominently from 

 the surface and are quite distinctly seen with the naked eye even in 

 young specimens. (The longitudinal muscles on the mesenteries of 

 embryos taken from the brood chambers are surprisingly well deve- 

 loped) (see fig. 20). Transverse sections of the muscle of the adult 

 specimen show (fig. 5) a compact mass of mesogloeal supporting 

 lamellee, many greatly branched and all invested with muscle fibres. 

 The parieto-basilar muscle (fig. 5, p.b.m.) is seen arising from the 

 mesentery some distance from the body wall, as the section is taken 

 rather low down near the foot disc. The arrangement of the 

 muscles on the mesenteries is quite regular — the longitudinal 

 muscles on the sides facing the intra-mesenteric spaces, and the 



