CONTRIBUTIONS ON THE MORPHOLOGY OF 

 THE ACTINOZOA. 



J. PLAYFAIR McMURRICM. 

 VI. HALCURIAS PILATUS AND ENDOCOPILACTIS. 



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. adc- 

 ncnsis, 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 Go nactinia prolifera. 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. 



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