ACTINIAN BUNODEOPSIS GLOBULIFERA. 311 



A vertical section through a portion of the base, inchiding a tangential section of a 

 mesentery, is represented in PL 25. iig. 2. On the mesentery the mesoglojal folds wliich 

 support the transverse muscle {traiis.m.) are strongly developed, and tlie muscle-fibres 

 are seen in section. At the basal termination of the mesentery, however, no foldings are 

 indicated ; the muscle-layer is here perfectly smooth. Sucli an appearance can scarcely 

 be regarded as in any way indicating an incipient basilar muscle, for no corresponding 

 development takes place on the opposite face wliich bears the retractor muscle. In such 

 sections, the muscle-fibres of the latter are seen lengthways. Where present in other 

 species the basilar muscle is, as a rule, arranged on more or less strongly developed 

 mesogloeal plaitings on each side of the insertion of the mesentery on the base, the 

 muscle-fibres extending in a radial direction. The present species is therefore character- 

 ized by possessing a parieto-basilar muscle of the weakest character, while the basilar 

 muscle is altogether undeveloped. 



The polyps are too small to permit of the presence or absence of mesenterial stomata 

 being determined by means of dissection. But in serial transverse sections iuterruiDtious 

 occur in all the perfect mesenteries close to the stomodseum and at its upjier extremity. 

 These represent the inner or perioral stomata, but no corresponding series has l)een found 

 near the column-wall, such as may represent the outer parietal stomata. 



Mesenterial Filaments. 



Mesenterial filaments occur at the free edge of all the mesenteries except the most 

 rudimentary. They appear on the complete mesenteries as these sever their connection 

 with the stomodgeum, while usually they are not developed on the incomplete mesenteries 

 until below the stomodoeal region. The filaments follow the contortions of the free edge 

 of the mesenteries, so that in the lower part of the polypal cavity the filament belonging 

 to one of the mesenteries may be seen cut through several times in the same section 



(fig. i). 



The filaments on the complete mesenteries are at first trilobed and exceptionally wide, 



and both the glandular streak and ciliated bands are clearly represented (fig. 18). The 



ciliated bands are far apart, and the tissue intermediate between them and the glandular 



streak is irregularly thickened, so that the outline assumed by the filaments is somewhat 



exceptional among the Actiniae, and varies greatly in different sections. A little within 



the base of the filament the mesenterial mesogloea divides into three very narrow 



branches, each of "which passes into a lobe, and there terminates in a clear expansion, 



practically devoid of any cell-enclosures. 



The middle portion of the trefoil is low, and the glandular streak at its apex 

 {g.s., fig. 18) is at first quite rudimentary in the degree of its development, merely capping 

 the middle of the filament as a more densely staining tissue. In addition to the 

 supporting cells, the glandular streak contains a few granular gland-cells and thick- 

 walled nematocysts. 



On each side of the glandular streak, and sharply separated from it, occurs an accumu- 

 lation of undifferentiated endodermal-like cells, rarely regu.lar in its outline, recalling in 



