Chapter One 



^Mechanics of Swimming 



IN CONSIDERING the characteristic modes of locomotion of any organ- 

 ism there are other factors besides simple progression to be heeded. 

 Perhaps the most important of these is posture, which in turn depends 

 largely upon bodily form as well as many environmental conditions. 

 The posture of an elephant and a mouse must be different, necessitating 

 differences in the skeletal framework and consequently in 'the muscular 

 equipment. Dissimilarity of muscular equipment involves correspond- 

 ing diversification of the controlling nervous mechanism, according as 

 a mammal may habitually trot, gallop, pace or hop. Muscular action 

 that is certainly reflex, if not actually involuntary in such forms as can 

 sleep while standing, is a necessary agent in maintaining posture in a 

 terrestrial mammal, while in a thoroughly aquatic one, such as a whale, 

 posture need not involve action of the muscles, and balancing actions 

 while moving are entirely different from those in which the non- 

 aquatic sort must indulge. Similarly there must be important modifi- 

 cations in the nervous equipment for determining the swimming ac- 

 tions of such a mammal as the seal as contrasted with that of the 

 sea-lion. 



The laws underlying the mechanics of swimming as employed by 

 vertebrates are of almost hopeless complexity for the reason that the 

 body is not rigid and the force is not applied at any one point, but 

 more or less continuously over a greater or lesser area. It has taken 

 many years to calculate the factors encountered by a rigid ship moving 

 through the water at a given speed with all the driving force applied 

 at one point. It has taken years for a multitude of highly trained tech- 

 nicians to discover the proper lines for a rigid aeroplane fuselage and 

 wings. If the latter were propelled to the accompaniment of con- 

 tortive wrigglings by the hinder end, or convulsive gyrations of the 

 wings by means of a multitude of small engines (i.e. muscles) of 

 unknowable horse-power delivering their power at vague points, one 

 may visualize how little would be known about aerodynamics at the 

 present time. Precisely this situation is encountered by one who would 

 investigate the principles underlying the swimming of mammals, and 



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