2 INTRODUCTORY [ch. 



brings into relation wdth itself: with every physical law and every 

 mathematical theorem which it learns to take into its employ. 

 Between the physiology of Haller, fine as it was, and that of 

 Helmholtz, Ludwig, Claude Bernard, there was all the difference 

 in the world. 



As soon as we adventure on the paths of the physicist, we 

 learn to weigh and to measure, to deal with time and space and 

 mass and their related concepts, and to find more and more 

 our knowledge expressed and our needs satisfied through the 

 concept of number, as in the dreams and visions of Plato and 

 Pythagoras; for modern chemistry would have gladdened the 

 hearts of those great philosophic dreamers. 



But the zoologist or morphologist has been slow, where the 

 physiologist has long been eager, to invoke the aid of the physical 

 or mathematical sciences ; and the reasons for this difference he 

 deep, and in part are rooted in old traditions. The zoologist has 

 scarce begun to dream of defining, in mathematical language, even 

 the simpler organic forms. When he finds a simple geometrical 

 construction, for instance in the honey-comb, he would fain refer 

 it to psychical instinct or design rather than to the operation of 

 physical forces ; when he sees in snail, or nautilus, or tiny 

 foraminiferal or radiolarian shell, a close approach to the perfect 

 sphere or spiral, he is prone, of old habit, to beheve that it is 

 after all something more than a spiral or a sphere, and that in 

 this "something more"' there lies what neither physics nor 

 mathematics can explain. In short he is deeply reluctant to 

 compare the living with the dead, or to explain by geometry or 

 by dynamics the things which have their part in the mystery of 

 life. Moreover he is little inclined to feel the need of ^uch 

 explanations or of such extension of his field of thought. He is 

 not without some justification if he feels that in admiration of 

 nature's handiwork he has an horizon open before his eyes as 

 wide as any man requires. He has the help of many fascinating 

 theories within the bounds of his own science, whieh, though 

 a little lacking in precision, serve the purpose of ordering his 

 thoughts and of suggesting new objects of enquiry. His art of 

 classification becomes a ceaseless and an endless search after the 

 blood-relationships of things living, and the pedigrees of things 



