692 Transactions of the Society. 



when we take into consideration the enormous differences in the 

 sizes of the spirals as seen in HtcksoneUa spiralis and Hicksonella 

 capensis. 



If then, the morphological origin of the unilateral disposition 

 of the polyps be admitted as possible, an explanation of the 

 spiral form assumed by such simple Alcyonaria and Antipatharia 

 may exist on this basis. In colonial Coelenterates the rate of 

 growth in the region of the polyps is always far in excess of 

 that in the non-polyp -bearing ccenenchymatous portion. This, in 

 part, accounts for the flabellate colonies^ so often met with in 

 Alcyonaria, but completely explains the flattening of branches of 

 species with bilaterally disposed polyps. On the other hand, in 

 large bushy Alcyonaria and Antipatharia it is always found that 

 the polyps are directed outwards, so that the unilateral growth 

 finds expression in all directions. In other words, the effect of 

 the unilateral growth in one series of branches is neutralized by 

 that in other series of branches growing in opposite directions. 



Let us now consider the case of simple colonies. 



1. In those whose polyps are disposed in four series, the growth 

 is in four directions in two planes at right angles to one another, 

 e.g. Sciiyearia quadrilineata, and these consequently neutralize one 

 another. 



2. In Juncella trilineata the growth is in three directions, each 

 of which encloses equal angles with the other. These also neutralize 

 one another. 



3. In other Juncellids the polyps arise in one plane, and are 

 therefore situated diametrically opposite, and the colony is there 

 still symmetrical. 



4. If, however, the polyps all arise on one side, the growth is 

 greater in that direction than in the other, and as the support in all 

 these cases is originally central, this will naturally result in an 

 overbalancing of the colony. 



Is it not possible that, in maintaining symmetry in the colony, 

 and also in endeavouring to expose the polyps equally to the food 

 supply (a feature seen in all colonial organisms), this excessive 

 growth might find expression in a spiral form (see pi. XIII. fig. I) ? 



LlTERATUEE ClTED. 



1889. Wright, E. P., & Th. Studer— Eeport on the Scientific Eesults of the 

 Voyage of H.M.S. ' Challenger ' (Zoology) xxxi. Alcyonaria. 



1904. Hickson, S. J. — Alcyonaria and HydrocorallinaB of the Cape of Good 



Hope. Part II. Marine Investigations in South Africa, i. No. 5, 

 pp. 67-96 (6 pis.). 



1905. Thomson, J. Arthur, & W. D. Henderson — Alcyonaria. Ceylon Pearl 



Oyster Fisheries Eeport, Eoy. Soc. London, pp. 271-328 (6 pis.). 

 1910. Simpson, J.J. — Eevision of the Gorgonellidse. I. The Juncellids. Proc. 

 Eoy. Irish Acad., August 1910. 



