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



As regards the systematic arrangement of the class Verrill's* labours are to be specially 

 noted. He has carefully distributed the numerous genera intc well-defined and 

 natural families, which he collects into the three suborders of Alcyonacea, Gorgonacea, and 

 Pennatulacea. More recently von Koch^ has published a classification of the Alcyonaria 

 based on certain anatomical details, dividing them into nine families, by which he 

 endeavours to ■ show forth their natural affinities. Hickson^ likewise with great 

 ingenuity has based a system of classification on the presence or absence of a ciliated 

 groove (siphonoglyphe) in the oesophagus of the polyps. 



A natural classification of a group should no doubt be the record of its evolution, and 

 should exhibit at a glance the stages through which the varied forms passed on their way to 

 the attainment of their present positions. A very thorough knowledge of the life history 

 of existing forms, and of the measure of their variableness, would be necessary ere the 

 outlines of such a classification could be attempted, and for the filling in of the details 

 one would require also a knowledge of extinct forms. Unfortunately for the perfection of 

 such a scheme among the Alcyonaria there is no appeal to palaeontology, the phenomena 

 which are of most importance, — such as the structure and relations of the canal system, 

 the structure and development of the individual polyp forms, — can never in fossil forms 

 be known, owing to their being incapable of preservation in tables of stone. 



We do not overlook the fact that in some cases the skeletal remains of forms such as 

 those of the Favositidse are to be met with, and that these, according to the convincing 

 researches of Moseley, appear to be nearly related to the still living forms of the 

 Helioporidse, nor that the Syringopora are related to the Tubiporidse, but these are but 

 instances rather of extreme differentiation of type, branch endings that afford no clue to 

 the peculiarities of the stem or root forms, presupposing generations of predecessors, whose 

 nature will probably remain for ever unknown. 



It follows therefore that there remains no other alternative but to trace out, as best 

 can be done on the existing available material, the probable evolution of the types, but 

 until much more is known as to the history of existing forms this cannot be done in an 

 eff"ective manner. Our first idea was to work out with this object in view the material 

 collected by the Challenger, but it soon became apparent that some of it was not 

 sufficiently well preserved for minute anatomical investigation, and that many important 

 types living in shallow seas, as well as those from the Indian Ocean and the north-west 

 coasts of America, were absent from this collection, so that we were forced to the 

 conclusion that it would be premature to do more than present such an orderly arrange- 

 ment of the group, as would for the present assist the student to a comprehension of 

 the new forms described in our Report. 



' A. E. Verrill, Proc. Essex Inst., vol. iv. p. 145. 



- G. V. Koch, Mitth. Zool. Stat. Xeapel, Bd. iii. p. 537. 



■* S. J. Hickson, Pliil. Trans., vol. cL\.\iv. p. 693. 



