AN ENTOPROCTAN POLYZOON (BARENTSIA BENEDENl). 837 



that this internode is the most flexile of all, for, while the others remain rigid, it may 

 sway to and fro, and may even curve itself into a circle. 



The early development of this form is more precocious than that of Barentsia 

 (Gonypodaria) ramosa, Eobertson, where, " by the time the calyx performs the function 

 of nutrition, it may have been carried into or above the second phalanx."* Here the 

 calyx is fully developed, but of small size, long before the first node shows any trace 

 of coming into existence. 



The sequence of the stages of development of the stalk appears to be as follows : — 

 The terminal thick layer of ectodermal cells is similar in appearance to that which forms 

 the growing point of the stolon, and here also functions as the centre of growth. The 

 terminal internode becomes greatly elongated by continuous growth, and from it is then 

 cut off the penultimate internode. This division is effected by two or three horizontal 

 rows of polygonal ectodermal cells which come into view lining the cuticle a short 

 distance below the diaphragm at the base of the calyx. These, by deposition of 

 chitin, strengthen the cuticle, and build up the chitinous septum which separates two 

 internodes. 



The minute structure of all the internodes is in general similar. Externally there 

 is a cuticle, varying slightly in thickness, and considerably in colour. Colourless, 

 transparent, thick and smooth immediately beneath the calyx, it becomes thinner 

 downwards. At the dilatations in the stem it is thick and wrinkled but still colourless, 

 while at the cone-shaped portions which occur on each side of the dilatations on 

 most internodes it is thick, rigid, and distinctly yellow in colour. The chitinous 

 wall consists of two layers, difficult to distinguish, the outer very thin, the inner 

 thicker, more highly refractive, and more readily stained ; in these respects the cuticle 

 agrees with that described by Ehlers in Barentsia ( = Ascopodaria) macropusA 

 There are no traces of " pores " in the chitin, such as Miss Eobertson has described in 

 Barentsia ramosa, and Ehlers in the species just mentioned. 



Lining the inner surface of the cuticle is a thin layer of regular ectoderm cells, 

 best developed just beneath the calyx, but insignificant except there and at the 

 growing points of stem buds. Beneath this, but confined to the dilatations of the stem, 

 are long muscle- fibres, arranged in a single-layered sheath and attached at either end 

 to the bases of the rigid chitinous cones. The greater portion of the interior of the 

 stalk, however, is filled by a gelatinous, hyaline matrix, scattered within which occur 

 connective-tissue cells, oval in shape and resembling those of Loxosoma rather than 

 those of Pedicellina.\ The mesenchyme is continuous throughout the whole colony, 

 perforations in the nodal septa allowing of its free passage from one internode to 

 another. 



* Robertson, Alice, " Studies in Pacific Coast Entoprocta," Proc. Californian Acad. Sci., ser. 3, vol. ii., part 4, 

 1900, p. 339. 



t Ehlers, E., "Zur Kenntnis der Pedicellineen," Abh. Konig. Ges. Wissensch. Gottingen, Bd. xxxvi., 1890, p. 16. 



I See Harmer, S. F., "On the Structure and Development of Loxosoma," Quart. Joum. Mier. Sci. (N.S.),' 

 vol. xxv., 1885, p. 277, pi. xix. figs. 5 and 10. 



