168 THE president's address. 



things which it cannot show us, forms of life the nature of 

 which we can only vaguely conjecture. 



Small wonder, then, if our knowledge of the invisible world 

 of organisms be still in a primitive state, especially as regards 

 the general lines upon which the simplest forms of life should 

 be classified. It is not too much to say that the classification of 

 the Protista has scarcely advanced, even amongst experts, beyond 

 a stage comparable to the popular classification of animals set 

 forth above. A certain number of groups are recognised, and 

 everything is expected to fit into one or another of them. If I 

 express my honest opinion that a spirochaete should not be 

 classified amongst the Protozoa, I am usually asked at once if 

 T think it should be placed in the group Bacteria ; just as the 

 statement made to an unscientific person that an earth-worm is 

 not an insect generally leads to the question whether it is a 

 reptile. 



In the great forests of the tropical zone there are many 

 species of animals of various classes belonging to what may be 

 called the tree-top fauna. Such are, for instance, the marmosets 

 in South America. We may imagine that a marmoset, born, 

 and brought up amongst the topmost branches of lofty trees, 

 might be ignorant for some time that the trees have stems, and 

 might never, in all its life, become aware that they have roots 

 also. Some chance hazard, such as the uprooting of a tree by a 

 storm or an earthquake, might reveal to it one day the remark- 

 able fact that the trees on which it had lived all its life have 

 roots, and if it were capable of reflecting on such a matter, it 

 might note with astonishment that the hidden roots were as 

 extensive in their ramifications as the branches exposed to the 

 light of day. 



We human beings belong, so to speak, to the tree-top fauna 

 of the organic world. Living amongst the highest branches of 

 the great tree of life, of which we like to believe ourselves to 

 be the topmost twig, the roots of the tree are buried and con- 

 cealed from us, until the microscope reveals them to our astonished, 

 gaze. Then we slowly become aware that the lowest forms of 

 life which constitute the vast group of the Protista are in their 

 range as extensive, in species as numerous, in character as varied, 

 and in mode of life much more so, than the familiar living 

 things of the visible world. 



