MAN'S ACCOUNT WITH THE LOWER ANIMALS 13 



indebted to the services of the zoologist, as witnessed by the 

 recent remarkable development of our knowledge of the 

 lowest forms of animal parasites, belonging to that great group 

 of microscopic organisms known as the Protozoa, such as the 

 malaria parasites, the trypanosome of sleeping sickness and 

 the amoeba of dysentery the importance of which is so great 

 as to have led to the recognition of a separate branch of semi- 

 medical study, to which the somewhat unfortunate name 

 Protozoology has been applied. 



Equally important, again, from the utilitarian standpoint, 

 is the study of the marine fauna of the world, regarded chiefly, 

 though by no means entirely, as a source of human food. 

 The great problem of our fisheries will be dealt with by 

 Professor Herdman, though he would be the first to tell you 

 that it is quite impossible to do justice to it within the compass 

 of a single lecture. An international organisation now exists 

 in Europe for the control of our fisheries, and an enormous 

 amount of research is devoted to the problem of maintaining 

 and improving our fish-supplies. I need hardly point out that 

 here again it is the work of the scientific zoologist, especially 

 in the study of the habits and life-histories, not only of the 

 fish themselves but also of the innumerable organisms upon 

 which they feed, that forms the indispensable foundation of all 

 future progress. 



I must ask you to turn now to another aspect of our 

 subject. What is it that, above all else, distinguishes a living 

 organism from the inanimate objects by which it is surrounded 

 and which therefore constitute the greater part of its environ- 

 ment ? It is the power of reacting towards that environment 

 in such a manner as to conduce to its own well-being ; of control- 

 ling, not only its own behaviour but also the behaviour alike of 

 its fellow-creatures and of inanimate objects, in its own 

 interests, and thereby maintaining its own position in the 

 universal struggle for existence. The humblest organism 

 exercises some control of this kind. A living bath-sponge, in 



