THE BUILDING OF REFLEX ARCS 237 



of such groups as those of Insects, Mollusca and Birds, and pass 

 on to the higher forms in which on the one hand function becomes 

 the predominant partner, and on the other individual experience 

 becomes more and more important. He feels indeed at liberty to 

 wish the entomologist and ornithologist all success, and to leave 

 him at peace, in his siding, to pursue his delightful and interminable 

 studies far from the dust and din of controversy. 



Insectivores. 



The critical territory of vertebrate, and still more of Mammalian 

 forms, in which the genealogist pictures the five main groups of 

 Insectivores, looking about them, if one may so speak, in the 

 world around and pondering which of many paths they shall pursue, 

 resembles certain centres that may be seen in towns where three, 

 four, five, or seven different roads are open to the traveller, each 

 with its incalculable effects on his ultimate career. If one may 

 change here the metaphor it may be said that the Insectivores are 

 the watershed of the Five Rivers of higher life. However much 

 the wayfaring insect-feeders have diverged from this broad centre 

 in structure, and however much the laws of genetics have widened 

 this divergence, the facts of function stare one in the face when such 

 descriptions of three of the four orders outside the Primate stock 

 are pondered — Flesh -feeders, Herbivorous animals, Burrowers and 

 Gnawers. These time-honoured names appealed strongly to older 

 zoologists, and in them is implicit a large body of evidence for 

 initiative in their evolution by pioneering work on the part of their 

 ancestors. Though in these days Prototheria include Monotremes, 

 One-vent animals, Metatheria, Marsupials or pouched animals, and 

 Eutheria Insect-feeders, and though Mammals derive their indis- 

 pensable name from the function by which they feed their young, 

 the most severe of systematists cannot clear his mind from the old 

 leaven of function in all these terms. They imply momentous 

 potentialities prior to new structures, and the modern fails to ban 

 entirely such functional names. I believe there is here no juggling 

 with names and words on my part, but a stone in the foundation 

 of the unambitious building which I am seeking to rear. It is 

 ultimately connected with a directive power as well as the formation 

 of sensori -motor arcs in the central nervous system. 



Is it possible or probable that the factors which led some group 

 to the water alone, some to a life in water and on land at different 

 parts of their lives, some to a crawling life on land and partly in 

 water, some to the air and trees, some to nocturnal, some to hyber- 

 nating, some to burrowing life, some to a diet of flesh, some to one of 



