1 1 



The mode of growth ot" Uie coenocciuiTi in C. levinscni is not at first sight api)arent. 

 The zooecia contain adult zooids, buds and developing embryos, any of which might conceivably 

 play tlieir part in the increase of the coenoecium or in the formation of new zooecia. I have 

 no actual evidence that the embryos take any such part, ])ut it is by no means impossible that 

 the\- may add a few lining lamellae to the proximal end of the tube, where they mostly occur. 

 The analogv of other fixed colonial animals suggests, however, that the embryos become free- 

 swimming and thus have the function of originating new colonies. I cannot find any indication 

 of bifurcation of the cavities of the coenoecium, or of the formation of diverticula which might 

 give rise to new zooecia. The explanation which appears to me most likely is that the buds 

 when Hberated from the parent stalks make their way out of the orifices of the zooecia and 

 crawl along the outer surface of the coenoecium until they find a suitable spot, where they 

 settle down and commence to manufacture their own zooecia. The crawling- movement would 

 prcsumably be effected by means of the anterior surface of the proboscis, a mode of locomotion 

 observed by Sars (72, pp. 9, 12) in the hving Rhabdopleiira. The proximal part of the entire 

 coenoecium is considerably thicker than the distal part, and it consists of a larger number of 

 zooecia. The increase in thickness can be accounted for by supposing that buds have commenced 

 their tube-forming activity on some part of the external surface of the coenoecium. The sup- 

 position is also in accordance with the fact that the proximal parts of the zooecia are constituted 

 partly by primary lamellae which are buried deeply within the coenoecium. 



In one or two parts of the colony, forming either the tip of the main a.xis, or a lateral 

 branch growing out from the axis, there are regions which are clearly young. This is indicated 

 by the paler colour of the gelatinous substance, and by the thinness of the walls of the zooecia, 

 which are here composed of primary lamellae only. The zooecia although less numerous than 

 in the more proximal parts are already obeying the same law of growth. They contain young 

 zooids (PI. I, fig. 5), of the form described on p. 18, which are already engaged in budding, 

 whilst their ovaries contain only immature eggs. In the more proximal parts of the colony, on 

 the contrary, there is but little budding activity, while ripe eggs are produced by the ovaries, 

 and mo.st of the zooecia contain eggs and embryos The hearing of these facts appears to me 

 to be as follows. In the proximal part of the colony but few buds are produced, and accordingly 

 the coenoecium increases in diameter comparatively little, the zooids expending most of their 

 energies in the production of eggs, which develop into larvae destined to found new colonies. 

 Nearer the growing tips there is a budding zone-, the buds on escaping fröm the zooecia 

 coming to rest near the bases of the existing peristomes, thus prolonging the coenoecium and 

 increasing its diameter. If the outflow of buds is sufficiently great at any point remote from the 

 apex of the coenoecium, a branch is formed. It must, however, be pointed out that I have 

 searched in vain for positive evidence as to the initial stages in the growth of a new zooecium. 



C. gracilis. (PI. II, hgs. 14—16. PI. V, figs. 54, 55). 



The slender coenoecium of this species, and its prostrate habit, are features which are 

 in marked contrast with those of the robust and erect species which has just been considered. 



