PREFACE 



A YEAR ago the University Press asked me to write a book 

 . which would make students of elementary Biology tliink. 

 I do not know in the least whether I have succeeded in doing 

 so. The average schoolboy, especially at the age when he 

 usually begins to study Biology, is strongly of the opinion 

 that "thinking is but an idle waste of thought," and with 

 few exceptions he turns away from the advice of one of the 

 wisest and worldliest of our teachers. "Of all the truths do 

 not decline that of thinking. The host of mankind can hardlv 

 be said to think," as Lord Chesterfield wrote to his son. 



What I have tried to do in this book is to emphasize the 

 unity of life, whether it be plant-life or animal-life, and the 

 interrelation of living organisms one with another and with 

 their surroundings. The crayfish with its scaphognatldtes and 

 dactylopoditeSy and the fresh- water mussel with its ctenidia 

 and its osphradia do not live self-contained lives tucked away 

 in water-tight compartments. They are in intimate relation 

 with the whole world of other plants and animals and with 

 their physical surroundings. The dead dogfish in a dissecting 

 dish gives one but little idea of what it did and of what 

 happened to it when it was alive. I have tried to bring out 

 the fact that plants and animals are at one in being alive, 

 and I have tried to make clear the intimate association of 

 both with their environment, whether it be the air or tlic 

 soil or the sea. The whole of life is so interwoven and inter- 

 connected that the "type-system," however well it may teach 

 us the rudiments of Anatomy, gives a totally inadequate 

 representation of life. 



