92 SECTIONAL ADDRESSES. 



In the earliest of these auimals the upper arm projected at right 

 angles to the body, and the forearm lay at right angles to it, nearly parallel 

 to the ground. The track was very wide, the stride absurdly short, and 

 only one foot could be moved at a time, whilst some of the muscles were 

 devoted entirely to the support of the weight of the body, lea\ang the whole 

 propulsive force to be supplied by the remainder or rather by such of them 

 as were not concerned with returning the limb to the position it occupied 

 at the beginning of the stride. From these slow and clumsy ancestors 

 we may trace the gradual acquirement of the structure found in Cyno- 

 gnathus or in a mammal ; where the arm moves nearly parallel to the princi- 

 pal plane of the animal, the stride is greatly lengthened and every muscle 

 contributes both to the support of the body and to its propulsion. 



Here we have a case where we can observe an improvement of an 

 animal mechanism which definitely enabled an animal to move faster than 

 its ancestor. 



But such general improvements in the mechanism of an animal's 

 body, which are the only adaptations which can be proved to have 

 occurred, differ so greatly in scale and in their general nature from that 

 detailed fitting of an animal to some particular niche in its environment 

 which Darwin believed to occur, that it is important to investigate whether 

 there is any general occurrence of such special relationship of structure and 

 habit and whether if it occurs it is rightly to be regarded as of adaptive 

 origin. 



It is, I believe, in the first part of such investigation that a good deal 

 of the future value of physiological work in zoology lies. 



The physiological work which is at present being conducted by 

 zoologists falls under two main heads. It may be concerned with the 

 explanation in physico-chemical terms of definite life processes, such as 

 fertilisation or cleavage, the activities of cilia or the nature of nuiscular 

 activity. Such work is of value to zoology because it increases our know- 

 ledge of the cell and all its parts and of the things which may control its 

 activities. It will become essential for an understanding of the factors 

 which underlie morphogenesis, that is of those factors some of which are 

 carried as material bodies in the chromosomes. But it is clear that it will 

 be long before even the fundamental phenomenon of cell di^dsion receives 

 its explanation ! Nevertheless, the present interest and ultimate value of 

 such fundamental researches is certain ; only through them can zoology 

 ever hope to approach its ultimate aim, the explanation of the Animal 

 Kingdom in terms of chemistry and physics, or the demonstration that 

 such explanation can never be adequate. But few zoologists have a suffi- 

 ciently wide knowledge of physics and chemistry to go far with them. 



The other type of physiological work is that which, like the classical 

 ' experimental physiology ' of the medical school, is devoted to an attempt 

 to iinderstand the functioning of the different systems of organs and ulti- 

 mately of the whole body of an animal. 



I believe that such studies hold out the greatest promise of results of 

 any in zoology. We do not laiow even as a first approximate the mode of 

 working of the body of any one member of the majority of the phyla of the 

 Animal Kingdom. 



We know a good deal about what is called ' Human Physiology,' that 



