COMPARATIVE ANATOMY AND MORPHOLOGY 339 



to function at the same time with an activity greater than the 

 average. If certain ones have a very great activity, they develop 

 beyond measure, but, correlatively, others become relatively inert 

 and atrophy. 



Principle of coordination or of correlation. As far down as life is 

 possible, there is every necessity that organs and their functions 

 should be bound together among themselves by mutual relations, 

 in a manner analogous to the wheels of a mechanism. Thus it is that 

 the elk could not carry the enormous weight of his antlers unless 

 the muscles of his neck had undergone a considerable develop- 

 ment. Other correlations, without resulting from physiological 

 necessities quite as rigorous, appear like the expression of very 

 general provisions. For instance, mammals which have hoofs are 

 herbivorous and have a large and flat maxillary condyle, and teeth 

 with a large crown striated with a crest of enamel, in order to tri- 

 turate plants as if between millstones; carnivores, on the contrary, 

 which have large canines, have a transverse condyle and a foot 

 with five digits provided with nails. It follows that it is possible, 

 to a certain extent, and sometimes with remarkable precision, to 

 deduce the formation of certain parts by that of certain others; 

 seeing the canine tooth of a lion, the hoof of a horse, the antlers of 

 an elk, we may divine the transverse condyle and the clawed foot 

 of the first, the flat condyle and molar teeth of the second, the 

 powerful cervical muscles and the cervical vertebrae with high 

 apophyses of the third. It is to Cuvier that we owe this principle 

 and its chief applications, and the same author's principle of the 

 subordination of characteristics is but another expression of the same 

 view. 



Principle of the division of labor. The general functions which 

 organisms must fulfill in order to live and reproduce their kind 

 are the same from one end to the other of the scale of beings. Simple 

 creatures which occupy the bottom of the scale fulfill their functions 

 almost without organs. The substance which constitutes their 

 bodies, protoplasm, possesses the rudiments of all the indispensable 

 properties; it assimilates and excretes, it feels, it moves, it divides. 

 As we mount towards organisms more and more perfect, we perceive 

 that the progressive perfecting has for its foundation the formation 

 of special organs more and more differentiated, better and better 

 fitted to accomplish in a more perfect manner a special work, and 

 less and less capable of performing multiple functions. Thus the 

 motile and nervous functions are divided between two very different 

 elements, the muscle-cell, possessing an energetic and rapid con- 

 tractility, but insensible, and the nerve-cell, incapable of energetic 

 movement, but well suited to receive impressions and to transform 

 them into motor impulses. 



