CONTRIBUTIONS ON THE MORPHOLOGY OF THE ACTINOZOA

Abstract

IN 1892 Carlgren showed that certain Edwardsiae, whose tentacles were more numerous than the mesenteries, had these tentacles arranged on the hexactinian plan, their arrangement in this presumably primitive group of the Actiniaria seeming to foreshadow what is characteristic of the phylogenetically later group. In other multitentaculate Edwardsiae he found what seemed to be an octamerous arrangement combined to a certain extent with hexamerism, but later studies (†99)con vinced him that the octamerism did not occur, and that in all cases the hexamerous arrangement obtained. In the mean time an important discovery had been made by Faurot (†95)in studying Edwardsia beautempsi and E. ade nensis, the former of which possesses fourteen to sixteen ten tacles, while for the latter the number is stated to be fifteen to sixteen. Sections through the column showed the eight mesen teries, which have long been supposed to be the only mesen teries developed in the Edwardsiae; but in the uppermost portions a number of additional very short and narrow mesen teries were found which in .E. beautempsi were placed in such a way as to make with the perfect mesenteries an arrangement recalling what occurs in Gonactinia prohfera. Thus there were eight pairs of mesenteries present in the upper part of the column, two of which, the directives, were formed of two per fect mesenteries, four of one perfect and one imperfect mesen tery, and one of two imperfect mesenteries. In E. adenensis the additional short mesenteries were arranged in pairs in each interval between adjacent perfect mesenteries, except in the endocoel of the directives, so that in this form the arrangement differed somewhat from that typical for the hexactinians.