LINNEAN SOCIETY OF LONDON. XXI 



vague and inconclusive ; and the assistance we can derive from the 

 geological record is so exceedingly slight, especially if we descend 

 below those tertiary times in which the ramification was not very 

 materially different from that now exhibited, that in the construction 

 of our tree much must be left to the imagination. Still, as real 

 affinities and geographical relations come to be more carefully 

 studied, and as here and there missing links are discovered, either 

 among geological remains or still lingering in some unexplored 

 region of the globe, we may yet hope gradually to obtain a fair out- 

 line of the lost ramifications of our dicotyledonous tree, provided we 

 are always on our guard against the common error of treating 

 plausible conjectures as established facts. 



Hiickel, in his Calcisponges, may have had a much better founda- 

 tion for his conjectural pedigrees than Strasburger in the Dicoty- 

 ledons ; for many of their races of a very early stage of development 

 appear to have descended to us unaltered, together with their primary 

 slightly modified branches and many other later and later more and 

 more diverging ramifications. The continuity through successive 

 ages and geological periods of the medium in which they live (the 

 bottom of salt water at moderate depths), their apparently absolute 

 independence of climate, may have brought down to us many of 

 these first ramifications of the Calcispongian trunk with com- 

 paratively few gaps or well-defined and isolated clusters, thus pro- 

 ducing that almost inextricable intricacy and indefiniteness in its 

 genera and species which critical botanists of our days observe in 

 the subspecies and varieties or minor ramifications of the Rubus 

 fruticosus trunk, which Nageli has so well shown to be the case with 

 the present species of Hieracimn, or which Carpenter illustrated 

 in the genera and species of the very ancient race of Foraminifera. 

 Hiickel has thus selected an excellent subject for his investigations, 

 and, as far as I am able to judge, has carried them through in that 

 masterly manner which, as attested by Huxley, characterized his 

 former work on Radiolaria. The volume containing the systematic 

 exposition and illustration of the Calcisponges bears evidence of the 

 most careful and persevering research during the five years he has 

 devoted to it, and is preceded by a most detailed account of the 

 anatomy, organology, and physiology of the group, upon the merits 

 of which it would be out of place for me to give an opinion. He 

 has also entered into some general considerations, worthy of the 

 study of all naturalists, as to the principles of natural and artificial 

 classifications, the former founded on hereditary affinity, to be 



