CXXVl INTRODUCTION. 



ently diagnostic, as we find a similar structure in 

 some Cheilostomata (e. g. Aetea) ; he also objects to the 

 union of tlie Halcyonellea and Stolonifera in a single group. 

 As to the latter point, he seems to me to have exaggerated 

 the amount o£ difference between these two sections. The 

 primitive forms of StoJonifer^a, such as VictoreUa, are very 

 slightly removed from those Alcyomdia in which the 

 cells are more or less detached and arranged in linear 

 series. In the former the erect, tubular portion of the 

 adult cell is a direct continuation of the stolon ; in the 

 young state this erect portion is wanting, and the cell is 

 wholly decumbent and in the line of the stolon. It is 

 essentially the same as a cell of Alcyonidium disjunctum 

 or of Arachnidium. If the fore part of the latter were 

 to be produced into a tubular extension (and this takes 

 place in some cases, as in Alcyonidium mamillatum and 

 Arachnidium fibrosum) , it w^ould be almost identical with 

 such forms as VictoreUa and Cylindroecium. In the higher 

 Stolonifera (such as Boiverbankia) the stolon must be re- 

 garded as made up of cells in Avhich the polypide is 

 aborted, and the true zoo3cium is the equivalent of the 

 tube of VictoreUa, which has gradually become contracted 

 below and isolated from the stolon. The two groups, then 

 are closely connected ; and there seem to be no sufficient 

 grounds for separating them. 



As to the second objection raised by Ehlers, I confess I 

 cannot see that the existence of certain obscure vestiges of 

 the setose operculum in a few forms occupying the border- 

 land of the Cheilostomatous division should be accounted 

 fatal to the present group. In the " frill " of the genus 

 Aetea the structure has entirely lost its original character; 

 and if this relic should indicate a not distant relationship 



