416 Mr Menem, Notes on Semper s Larvae. 



With regard to the relation of the Zoantheae to other groups, 

 Van Beneden, after a most careful study of Semper's first larva, 

 came to the conclusion that the Zoantheae are not related to the 

 Actiniaria through Edwardsia, but that they form a group quite 

 distinct from the others. McMurrich, Boveri, and others, on the 

 other hand, consider that the Zoantheae are allied to the other 

 groups and derive them with the others from a common Edwardsia 

 stage. Goette in a recent contribution is inclined to unite them 

 with the Ceriantheae and the Antipatharia, and to derive them 

 from a common hexamerous type, while all the other Anthozoa 

 are derived from a common octomerous type. 



It seems impossible to maintain that the Zoantheae are derived 

 from an Edwardsia type. Whatever the relations of this group 

 to the other groups associated with it by Goette may be there 

 can be no doubt that it is widely separated from the Actiniaria 

 which are derived from the Edwardsia type. As the six-mesen- 

 tery stage is the characteristic stage in their development, the 

 Zoantheae have to be derived from a hexamerous type. In as 

 much as the six mesenteries of this stage are homologous with 

 the first six mesenteries of the Edwardsia stage, the two types 

 must be considered to have had a common line of descent. While 

 the Zoantheae branched off from the main stem at an early stage 

 (the six-mesentery stage), the other groups did not branch off till 

 a later stage (Edwardsia) when there were eight macromesenteries. 

 In connection with this early isolation of the group it is interest- 

 ing to note that the larvae of the Zoantheae have retained what 

 must be considered a primitive feature in their longitudinal and 

 transverse ciliated bands. These bands are vestiges of a condition 

 common to the ancestors of the Anthozoa and the Ctenophora, and 

 characterised by the presence of longitudinal bands of long cilia 

 in addition to a uniform covering of small cilia. In the Cteno- 

 phora these bands became modified to form the eight rows of 

 swimming-plates. In the larvae of the Zoantheae they were 

 reduced to a single band, or to their oral ends which fused 

 together to form a circular transverse band. 



REFERENCES. 



(1) E. Van Beneden. Une Larve voisine de la Larve de Semper. 

 Archiv Biol. Tom. x. 1890. 



(2) McMurrich. On the development of the Hexactiniae. Abstract 

 in Zoologischer Jahresbericht, 1891. 



(3) A. Goette. Einiges iiber die Entwickelung der Scyphopolypen. 

 Zeit. wiss. Zool. Bd. 63, 1898 (pp. 354 and 357). 



