220 J- Playfair Mc Murrich, 



cestral conditions and it is tliese wliicli furnisli tlie basis for tlie 

 Classification of the varioiis forms within the group. For instauce, 

 the occurrence of paired bipinnate ctenidia may be regarded as an 

 ancestral character in the Mollusca and they constitute persistent 

 characters in certain members of the group; and yet the grouping 

 togethei' in one order of all those Mollusca which present this pe- 

 culiarity, ignoring all the progressive modifications which they may 

 show, would constitute an arrangement which would appeal to no 

 one. Rather do we use the progressive characters as a guide for 

 the Separation of the group into subgroups at the base of each of 

 which we place those forms in which persistent characters are most 

 perfectly developed. 



In the Actiniaria, it seems to me, we have similar conditions. 

 The ectodermal musculature of the column wall represents a per- 

 sistent characteristic and if not associated with marked progressive 

 characters may well serve as a guide to the more primitive mem- 

 bers of the group. But if associated with such peculiarities it is no 

 longer possessed of prime classificatory importance, and to group to- 

 gether all forms which possess it, independently of their progressive 

 modifications, is as incorrect as would be a corresponding Classifi- 

 cation in the Mollusca, Certain of the Actiniaria which possess the 

 musculature are nndoubtedy to be regarded as primitive, or as re- 

 presenting primitive conditions, such for instance as Gonadinia and 

 Protanthea. But, on the other band, such forms as Boloceroides mac- 

 murricM and Bolocera brevicornis ^) it is associated with the multipli- 



1) Carlgren (1902) has expressed himself as very skeptical regard- 

 ing the accuracy of my statement that ectodermal loagitudinal muscles 

 occur in the column wall of Bolocera brevicornis and regards that species 

 as identical with B. tnulticornis Verrill. I can assure him, however, 

 that there is no room for doubt as to the existence of the musculature. 

 It is true that the epithelium of the column wall was largely macerated 

 away in the specimen I exarained and this led me to regard the irregul- 

 arity of the surface of the mesogloea as the result of the maceration. 

 Where, however, the epithelium is retained in spots the irregularities are 

 clearly muscle-bearing processes of the mesogloea and the presence of an 

 ectodermal musculature is even more distinct than in Protanthea. 



As to the identity of brevicornis with iimlticornis, I may say that 

 when I described the former I had preparatious of miiUicornis before me 

 for comparison and the two forms seemed to me to be distinct. If, how- 

 ever, the view of my colleague as to their identity be accepted, an ex- 

 planation of how one individual of a species may belong to the Nynantheae 

 and another to the Protantheae is in order. 



