32 Coelenterata. 



mesogloea. The stomo(heum has very thick walls. The apical end of the axis 

 projects into the space between the two dorsal mesenteries. The 4 axis-septa 

 have not the slightest relationship to the mesenteries of the end-polyp; this 

 polyp is, therefore, not the primary polyp, but is a secondary lateral one which 

 has assumed the terminal position. There is an axis-epithelium, which agrees 

 histologically with the rest of the endoderm. The zooids of this Pennatulid are 

 much reduced. - Umbellula. In pellucida the 4 principal canals extend to 

 the lower end of the stalk, and are in communication by means of perforations 

 in the intervening septa. In the blind sac which forms the axis-sheath there 

 are 4 longitudinal canals, separated by septa. In antarctica the septa between 

 the 4 principal canals are thick and contain numerous cords of cells. These 

 4 canals are connected here and there with the peripheral network, which 

 consists largely of longitudinal parietal canals, partially separated from each 

 other by incomplete radial lamellae. In pell, the longitudinal musculature is 

 well developed in the lowest part of the stalk, and the circular muscles are 

 also clearly seen. Higher up the stalk the circular muscles are massive, but 

 the longitudinal ones are reduced. In the polyp-cluster a colonial musculature 

 is not present, but the muscles of the polyps are strongly developed. At the 

 lower end of the axis, and within the axis-sheath, there are horny cords, arising 

 as in Ftin., which become united to the axis. An axis-epithelium was not 

 recognisable. In its lowest part the axis consists of weakly cornified cords, 

 in which the remains of cells are present. The axis just below the polyp- 

 cluster contains a central canal filled with gelatinous substance, and surrounded 

 by a layer of slightly cornified connective tissue. Around this is a layer, 

 almost cruciform in section, of very closely packed concentric horny lamell*, 

 and oiitside this a layer of less closely disposed lamellae with radial markings. 

 In the intervals between the 4 arms of the inner portion of the axis there are 

 more or less horny cords. The axis is enveloped in a thin connective tissue 

 sheath, and an axis-epithelium is not recognisable. There is also horny sub- 

 stance on the outer side of the axis-sheath, and at the points of insertion of 

 the 4 septa on the axis-sheath. The axis of antarct. lies in a strongly devel- 

 oped sheath, in which the 4 septa are inserted. The matrix of this sheath 

 stains more deeply than that of the septa and is traversed by a network of 

 strong fibres. In this network there lie imbedded numerous cords, which gra- 

 dually merge into the endodermal cell-cords of the septa. The nearer these 

 cords lie to the axis the more do they exhibit cornification. In one large 

 polyp there was a small and short siphonoglyph. The zooids in the polyp- 

 cluster have no musculature either in their mesenteries or in their body-wall. 

 The zooids of the stalk are much smaller than those of the cluster, and have 

 no trace of tentacles; septa are present only in the upper part of the zooid, 

 and mesenterial filaments are wanting. The coelentera of these zooids open 

 directly into the peripheral canal-system. The 4 principal canals terminate 

 above in the much folded axis-envelope; they are not connected with the 

 coelentera of the polyps. The mesogloea of the polyp-walls is very thick. In 

 the lowest part of the stalk there are several funnel-shaped openings in the 

 ectoderm; each of these is provided with a sphincter, and leads into a canal 

 (probably ciliated) which opens into one of the principal canals. - Virgularia. 

 The radial canals do not open to the exterior, and are fundamentally different 

 from the ciliated canals of Scytaliopsis. In the lower part of the stalk of 

 juncea,) horny cell-cords are present in the thick inner mesoglceal ring, lying 

 in groups and exhibiting clearly their origin from cords of endoderm cells. 

 The accessory axis, occasionally found in V., may have arisen by union of 



