76 



EXPLA.NATORY. 



The lowest organisms are placed at the foot of the Table, the highest 

 at the top. The line, straight or zig-zag, traced from the very base 

 upwards to any name indicates the probable course of the evolution of 

 the group of animals to which the name belongs. If a line stretches 

 upwards it shows an advance in structure; if it is nearly horizontal it 

 means that Uttle or no upward evolution has taken place ; if it slopes 

 downwards, that indicates degeneration or degradation. The propor- 

 tional lengths and angles of the various lines are meant to represent 

 roughly the amount and the nature of the evolution which has taken 

 place. 



In no case has the line representing the evolution of one group 

 been allowed to pass through another group. All existing animals 

 are represented as being at the ends of lines or branches. 



Most of the larger groups or phyla have been enclosed in dotted 

 red lines in order that their limits might be easily seen at a glance. 



It is scarcely necessary to point out that horizontal lines could not 

 be drawn across this table in such a way as to divide it into sections 

 representing the Fauna of the various geological periods. In order to 

 show that, a very different table would require to be constructed in 

 which distance along a line stretching upwards from the base* would 

 indicate merely the age of the group and not evolution or advance in 

 organisation as in the present table. Degeneration could not be 

 represented, and it would be impossible to distinguish except, perhaps, 

 by colour, between groups which had undergone rapid evolution and 

 those which had remained comparatively stationary. 



* In such a table the Foraminifera and other groups of Protozoa would extend 

 from the base to the top of the table, although they have undergone comparatively 

 little evolution. Some of Haeckel's phylogenetic schemes (see Generelle Morpho- 

 logic der Organismen, Berlin, 1866) are of this palaeontological nature and show the 

 probable distribution in time of the various groups of animals and plants. 



