6 Proceedings of the Royal Irish Academy. . 



The extraordinary power of regeneration as seen in this group is of great 

 physiological interest. Normally they are attached to rocks or corals ; but 

 even shells — e.g., Manjaritifera margaritifcra — may form a basis of support. 

 Ridley records the case of a colony in the " Alert " Collection which had been 

 broken from its attachment, and in which the eoenenchyma had quite- over- 

 grown the fractured part, which had continued its existence as a free 

 colony, floating in the ocean. A similar case has been recorded by the 

 writer for Ids Mppuris (Journ. Linn. Soc. Zool., vol. xxxvii., pp. 421-433, 

 pi. 43). 



These large Juncellid colonies also form bases of attachment for numerous 

 kinds of animals. Ophiuroids and crinoids are constantly found attached to 

 them, but equally common and more pei-manent are acorn-shells and bivalves. 

 The former settle down in the larval stage, bore their way through the 

 eoenenchyma, and i-emain attached for life to the axis. The Alcyonarian 

 colony responds to the stimulus, and continues to develop eoenenchyma at 

 the fractured part, so that eventually the acorn-shell is quite overgrown by 

 polyp-bearing eoenenchyma, leaving only a small oval aperture, by means of 

 which the acorn-shell derives its food — a characteristic form of commensalism. 



Of more economic interest, however, is the case of Pteria macroptera, 

 which is eagerly sought for on account of its pearl-bearing proclivities. 



While examining the marine fauna of the Mergui Archipelago, one of tlie 

 most striking phenomena encountered was the fact that on nearly every 

 colony of JmiccUa gemmncea obtained there were abundant specimens of this 

 oyster. Some idea of the strength of these colonies may be gathered from 

 the fact that on one individual colony there were over a hundred oysters. 

 The greater number of these were almost full-grown, and each of them 

 weighed on an average more than the colony itself. The liyssus was usually 

 overgrown by eoenenchyma; but the great rate of growth of the shell itself 

 precluded the possibility of the Alcyonarian keeping pace with it. 



Reproduction. — A large proportion of the colonies examined contained 

 enormous spherical reproductive bodies. Serial sections of some of the.se 

 were made; aud Professor Hicksou also kindly sent me some sections prepared 

 by him. These bodies consisted of two kinds : — 



(1) Ova with a large nucleus and a distinct nucleolus almost identical 

 with the figures given by von Koch. 



(2) Spermathecae or sperm sacs in whi(;h it was possible to trace 

 spermatogenesis almost up to the stage of fully formed spermatozoa. 



No trace of segmentation of ova was discernible; and it is more than 

 probable that this does not take place within the parent body. 



It is also worthy of note that the ova and spermathecae occurred in 



