158 MCMURRICH. [Vol. V. 



is evidence that the colonial growth, and the development of 

 the axis and spicules, have been acquired since the establish- 

 ment of the group, since we know such simple forms as Monoxe- 

 nia, Hartea, and Haimea ; and as to the development, we know 

 practically nothing of that of these simpler forms, a study of 

 which may, perhaps, reveal a succession of mesenteries instead 

 of their simultaneous appearance. The peculiarities of the mes- 

 enterial filaments seem to be the greatest difficulty ; but even 

 here it seems quite possible that the difficulties may vanish or 

 be diminished with a better knowledge of these lower forms, 

 since Haacke ('84) states that in Xenia the arrangement of the 

 filaments differs materially from what E. B. Wilson ('83) has 

 described in Paralcyonium, etc., and more nearly approaches in 

 some respects what is found in the Actiniaria, though the extent 

 of the similarity is not fully brought out in the brief communi- 

 cation which is all Haacke has contributed on the subject. 



The fact that Andres ('80) has stated that the respiratory 

 portion of the mesenterial filament is absent in E. Claparedii, 

 and that we have no definite information concerning its presence 

 in any of the other forms that have been studied, might lead one 

 to infer that the respiratory portions of the filament of the Hex- 

 actiniae had nothing to do phylogenetically with the respiratory 

 filaments of the Alcyonaria. This is negatived, however, by the 

 fact that the respiratory filaments do occur in certain Edwardsiae, 

 as I have been able to find them in an undetermined species from 

 the Pacific ; and if they are absent in E. Claparedii, and even in 

 other forms, this must be regarded as a secondary condition. 



What is needed to determine this question is a careful and 

 comprehensive study of the filaments of the Alcyonaria, espe- 

 cially of the simpler forms. In the meantime, I am inclined to 

 consider the Alcyonaria as forms which have branched off from 

 an Octactinian ancestor which they had in common with the 

 Edwardsiae, and that they approximate this ancestor in the ar- 

 rangement of the mesenterial musculature, and in the nature of 

 the siphonoglyphe more closely than do the Edwardsiae, but in 

 other points, such as the tentacles, the skeleton, and the mesen- 

 terial filaments, they show a marked specialization, which has 

 occurred within the limits of the group, that is to say, since 

 the Edwardsiae branched off from the main line, leading from the 

 Octactinian ancestor to the Alcvonaria, as we now know them. 



