V. APPENDIX. 



ON THE USE OF A GENEALOGICAL TREE. 



A genealogical tree of the animal kingdom, even if drawn with perfect 

 biological accuracy, can only represent the lines of life as seen projected 

 on a plane surface. Thus, two groups, apparently close together, may 

 be far asunder, the one above, the other below, the surface. 



Nevertheless the " Tree " may be of some service in suggesting 

 analogies or affinities unlikely to be noticed at close quarters ; just as 

 the outline of a range of hills may best be seen at a distance. 



If a similar tree- of the vegetable kingdom were before us, we might 

 observe in it a division, Protophyta, answering to Protozoa ; and a 

 group, which may be termed the Vaucheria group, including Sijihonece 

 and PA?/^*'''*^/'^^^^*' 'corresponding in some striking respects with Vermes. 

 Degradation through parasitism would appear to be less prominent, 

 and change throu,yh adaptation to environments, more conspicuous, 

 than in the classes of animals. The most remarkable feature in the 

 two pedigrees might, perhaps, be recognised in the fact that they are 

 so distinct, the one from the other. From the simplest forms, and the 

 most remote ages, of life on the earth, the two kingdoms of animals 

 and plants have been developed side by side, without coalescence or 

 confusion, though having protoplasm, absolutely indistinguishable by 

 experiment, as a " physical basis of life," common to every constituent 

 of both kingdoms. 



As favouring such generalised conceptions of unity in Nature, a 

 Genealogical Tree may have its use ; though sharing, in common with 

 all other appliances, an incapacity for adequately representing the 

 details or the method of scientific classification. 



