EVENING DISCOURSES. 819 



The wonderful harmony existing between the form and functions of a muscle, 

 the marvellous co-operation of groups of muscles to produce .specific movements, 

 are revealed everywhere in animals as well as in the human frame itself. The 

 co-ordination takes place in the higher animals in the central nervous system, 

 a system characterised by autonomy as well as centralisation, a system so com- 

 plex that a few years ago its main highways could only be guessed at, but 

 which now, thanks to the labours of experimental physiologists, pathologists, and 

 histologists are as well known as the great high-roads that intersect the country 

 itself, and they are maintained in a far more workable condition than obtains even 

 in the best roads. We also know the side-paths from these main nerve tracks, and, 

 thanks to the genius and researches of Sherrington, we have reached a measure of 

 finality, for have we not in reflex actions a ' final common path ' towards which 

 converge a multiplicity of private yet ever open and serviceable paths with a free 

 right of way? Orderly 'behaviour' characterises the outward visible movements 

 of animals, as well as the sequence of events in the internal, invisible motor organs 

 on which the continuance of life itself depends. As the movements of animals are 

 intimately related to their habits and modes of life, this opens up another aspect 

 of the question. 



Animal movements may be classified according to the media on or in which the 

 animal moves. In terrestrial progression the ground is a more or less fixed or 

 rigid point of support or fulcrum. The action of the moving limb tends to repel 

 the fulcrum in one direction, and the body itself in the opposite direction. The 

 more solid and resistant the ground, the greater will be the amount of energy 

 available to propel the body forward. The energy, however, is generated by the 

 animal itself. Everyone knows how little progress he makes on a shifting, feebly 

 resisting surface such as sand. In aquatic progression, as in the swimming move- 

 ments of a fish, the fulcrum is the water, which is freely mobile and easily dis- 

 placed, so that much of the energy is dissipated in moving the water itself. The 

 specific gravity of a fish is approximately that of the water itself. Some animals 

 are moved by the expulsion of water from the body — in the jelly-fish the bell con- 

 tracts and forcibly expels water, while the cuttle-fish expels the water in its mantle 

 through its funnel. The animals are propelled in an opposite direction. The 

 lowest microscopic water-dwellers move by indefinite limited contractions and 

 expansions of the protoplasm, of which their microscopic bodies are made up. 

 Others are propelled by the rhythmical vibrations of cilia on their surface or by 

 the undulations of a membrane. 



As air is eight hundred times lighter than water, aerial motion presents the 

 most interesting of all problems. It has been solved by insects and birds alike, 

 and both of these flying motors are heavier than air. The air fulcrum is far more 

 mobile than the aquatic or terrestrial support, yet in spite of this the greatest 

 velocities are obtained in aerial progression. 



If we adopt a more popular classification, depending on the number of legs 

 possessed by animals, we have bipeds, quadrupeds, centipedes, and even millipedes. 

 In these hundred-footed creatures the marvellous co-relation of their segmental 

 limbs excites our wonder, while the exact analysis of the sequence of movement 

 almost baffles our methods of study. Some of you know the disturbances of 

 motor acts that are produced in human beings when a person is mentally excited, 

 or on occasion when he may be the object of scrutiny by an onlooker. 



Borelli. De Motu Animaliitm. 



In the seventeenth century there began that glorious period of scientific 

 endeavour and achievement, the period of Harvey, Galileo, Torricelli, Malpighi, 

 Redi, and Stensen, the period when new methods were applied to the study of 

 physics with such brilliant results. In a humble convent cell in the monastery 

 of San Pantaleone in Rome, on the last day of the year 1678, and as the New Year 

 was coming in, there died the founder of the Study of Animal Movement, 

 Giovanni Alfonso Borelli. He was born in Naples in 1608, the son of a Spanish 

 soldier, and a Neapolitan mother, whose name was Borelli. His name stands in the 

 forefront as a great pioneer and founder of the study of animal movement. After 

 being educated in Rome he became professor of mathematics in Messina about 

 1640, and in 1656 he was called by Ferdinand'Duke of Tuscany to Pisa, where he 



