30 Coelenterata. 



colonial musculature is present only in the stalk, and is situated on the inner 

 side of the outer mesogloeal ring. It is supported by very numerous, but not 

 high, radial lamellae, which vanish as the stalk merges into the Kiel, and 

 with them disappear also the muscles. The circular musculature is comparatively 

 feeble, except in the upper part of the stalk, and near the sphincter pedunculi. 

 In eleg. the longitudinal muscles extend into the Kiel. In obesa the mus- 

 culature is much stronger than in the other two species, and in the neighbour- 

 hood of the sphincter is especially powerful. A strong colonial musculature is 

 present throughout the Kiel. The longitudinal muscles lie in separate groups 

 below the canal system connecting the zooids. A cubical axis-epithelium is 

 clearly visible. The zooids of pus. are extremely small; each has a highly 

 developed siphonoglyph, but the septa are small, being restricted to the upper 

 part of the zooid, and have no musculature. The zooids of eleg. and obesa 

 are larger, their septa are relatively strong, extend further down the ccelenteron, 

 and, in their lower portions, bear well developed muscles. The ccelentera of 

 the zooids are in connection with each other by wide branched canals, and 

 with the polyps by numerous short but wide canals. Veretillum. The mus- 

 culature of the stalk of cynomorium is unusually strong. The buds described 

 by Bujor [see Bericht f. 1901 Coel. p 15] are typical zooids. Communication 

 between the coelentera of the zooids and polyps takes place almost exclusively 

 by the canals of the spongy tissue, which surrounds, and is connected with, the 

 4 principal canals. Echinoptilum. In echinatum there are, in the lower 

 part of the stalk, only 2 canals (dorsal and ventral) connected by perforations 

 through the septum. About the middle of the stalk the septum becomes thicker, 

 and a little higher there appear within its substance the 2 lateral canals, which 

 are at first very small, but enlarge rapidly. In the region where the naked 

 portion of the Kiel narrows, the lateral canals become very much smaller, 

 and remain so in the upper part of the colony. Some distance below the tip 

 of the colony they vanish, then the ventral one disappears, and finally the 

 dorsal one. In the upper region of the stalk there are 2 short but wide accessory 

 canals, one above the other; one arises from the ventral and the other from 

 the dorsal principal canal. They lie in the dorso-ventral septum, from which 

 their upper ends protrude, as blind sacs, into a lateral canal. These accessory 

 canals, which lie in about the same position as the axis in other Pennatulids, 

 and the axis-sheath of axis- bearing Pennatulids have a common origin, namely, 

 from endoderm cells, which, as a cord or canal, traverse the central mesoglcea 

 where the septa of the principal canals meet. The colonial musculature is 

 highly developed, and about the middle of the stalk there is a strong sphincter 

 pedunculi, in which the circular muscles are much increased. In the transitional 

 region between stalk and Kiel the longitudinal musculature becomes divided 

 into separate bands, two of which are strikingly developed, that in the mid- 

 ventral line being especially strong. Its contraction is the cause of the ventral 

 curvature of the colony; it therefore serves as the retractor of the colony. 

 The antagonistic muscle is in the mid-dorsal line. The coelentera of the polyps 

 and the chief canals (especially the median ones) are connected with the inter- 

 vening network by short canals (possibly ciliated), the wall of each of which 

 is surrounded by a sphincter muscle, by which, doubtless, the connecting canal 

 can be closed. - - Actinoptilum molle agrees with Ech. in the arrangement of 

 the canal system and of the musculature of the Kiel (which is, however, 

 feebler in A.) t but differs in the musculature of the stalk; and blindly ending 

 accessory canals were not observed. Renilla. A comparison of the canal 

 system with that of Ech. reveals an unmistakable similarity (the lateral canals 



