2 THE VOYAGE OF H.M.S. CHALLENGER. 



recent discoveries have led to the exhaustion of the more comprehensive reforms of the 

 system of Corallia, as up to the present time we only know the structure of the soft parts 

 of tin' I mily, especially of the septa, from a comparatively small number of species, and 

 our knowledge, even of such forms as have been most thoroughly investigated, is far 

 from satisfactory. 



This also holds good for the soft-membraned Anthozoa, the Actiniaria or Malaco- 

 dermata. In this section the structure and arrangement of the septa are of the highest 

 importance for the proper comprehension of the structure ; they will probably require to 

 be taken pre-eminently into consideration in the classification, not only of the Actinia? but 

 also of the other Hexacorallia. But how little do we know on this point. In a recently 

 published work (Studien zur Bliittertheorie, Heft i., die Actinien, Jenaische Zeitschrift, Bd. 

 xiii. p. 457, 1879) my brother and I have tried to show that all the important charac- 

 teristics have hitherto been properly estimated only in a treatise by Schneider and 

 Rotteken (Ann. Mag. Nat. Hist., ser. iv., vol. vii. p. 437), and that, on the other 

 hand, both v. Heider (Sitzungsber. d. Kaiserl. Acad. z. Wien, Math. Nat. Classe, Bd. lxxv., 

 Abth. 1, p. 367, 1877), in his otherwise very elaborate anatomy of Sagartia troglodytes, 

 and Jourdan (Annales d. Sciences Nat., Zool., ser. vi., t. x., No. 1, 1880), in his treatise 

 on the Actiniae of Marseilles, remain far behind the two first-named naturalists. As, 

 however, we have only a short report in a preliminary publication on the researches of 

 Schneider and Rotteken, which extend over a large number of species, it is impossible 

 to make any systematic use of their material, and therefore the number of more detailed 

 anatomical studies of Actinia?, which, taken from different species, would enable us to 

 form an exhaustive plan of the variations of the type common to all, is still incomplete. 

 These anatomical studies we must have before we can deem it possible to settle an 

 accurate point of view from which to determine the relations of the Actinia? both to each 

 other and to the other Anthozoa. 



Since it appeared to me a grateful task to make a beginning myself in the direc- 

 tion just mentioned, I accepted with pleasure the offer made to me to undertake the 

 working out of the Actinia? collected by the Challenger Expedition. I wish at the same 

 time to express my most hearty thanks to the late director of the Challenger Commission, 

 Sir Wyville Thomson, and his first assistant and successor, Mr. John Murray, for the 

 great liberality with which they placed the rich material collected at my free disposal. 



Before going into a description of the separate species, I think it advisable to 

 determine in a few words the requisites, which, according to my view, ought to be fulfilled 

 by the anatomical description of an Actinia if this is to be of any systematic value. I 

 >>liall therefore preface the description by a sketch of the structure of this animal, in which 

 I shall lay stress upon the points which are most subject to variation, and to which the 

 special attention of the describer must be directed. Such an attempt is also to be 

 recommended for the further reason that in this way the reader will at the same time 



