14 



W. G. RIDEWOOD. 



the ostium, are common (Harmer, 10,' p. 9 and fig. 12). The disposition of these rings, 

 complete and incomplete, is more clearly marked in C. levinseni than in C. nigrescens, 

 for in the latter the common portion of the test that fills in the interval between one 

 tube and the next (" external secondary lamellae " of Harmer) is more abundant, and 

 only the terminal portions of the tubes stand out freely. The mode of deposition of 

 the material in C. nigrescens is illustrated in figs. 12 and 13 of plate 4, and reference 

 to the latter of these will show that not only may the secreted material spread over 

 from the tube-margin to the interval between the tube in question and its neighbours, 

 but that thin films are continued down the inner surface of the tube (" inner secondary 

 lamellae" of Harmer). These secondary lamellae, both inter-tubular and intra-tubular, 

 appear to have no existence in Rhabdopleura. 



TEXT-FIGURE 7. Rhabdopleura normani. A, portion of a colony, highly magnified. (Copied from Lankester, 

 13, plate 39, fig. 1.) B, terminal portion of a tube, more highly magnified. (Copied from Harmer, 10, 

 plate 2, fig. 19.) 



a, extremity of a growing branch ; 6, gymnocaulus or soft stalk of the terminal polypide of the growing branch ; 

 c, latest bud produced by the gymnocaulus ; d, penultimate bud ; the part of the stalk which produced it has 

 now become hardened, and is known as pectocaulus ; e, third bud ; it has forced its way through the wall of 

 the axial tubarium, and is constructing a lateral tube ; /, fourth bud, counting from youngest ; it is now a 

 fully-formed polypide, with complete polypide-tube with recumbent and vertical portions ; g, fifth bud ; k, 

 pectocaulus ; j, j, septa of axial portion of tubarium. 



The mode of bud-succession of Rhabdopleura is not paralleled in Cephalodiscus. 

 The terminations of the branching colony of Rhabdopleura are, as Lankester has shown, 

 of two kinds, those which are continuing to grow and produce buds (text-fig. 7, A, a), 

 and those which stand out at right-angles to the general plane of the colony and are 

 occupied by adult polypides (/ and g}. The proliferating stolon in the branches 

 of the former kind has no hard covering such as is found on the organic stalk that 



