40 BIOLOGY. [Book r. 



stance slowly contractile, which seems to be the rudiment, still 

 undivided, of the muscular fibre; it is a sort of non-figurate 

 muscular matter. This matter is called sarcode. 



There seems to be in inferior beings a confusion of organic 

 materials and functions. Many of the infusoria are endowed 

 with motility and sensibility, with a sort of instinct, and yet 

 they are destitute of muscular elements and nervous elements. 



We can place in a degree immediately superior the plants and 

 the animals simply polycellular, that is to say, constituted of a 

 certain niimber of cells similar to each other and grouped. They 

 are beings formed of a single tissue. 



On the other hand, at the outset of their embryological exist- 

 ence, the beings the most complex, the superior animals, man 

 not excepted, commence by being monocellular, then pass through 

 the polycellular state, the most rudimentary ; finally, in a last 

 period, their histological elements differentiate. 



This gradual histological differentiation, which is observed in 

 the embryological development of superior beings, can also be 

 demonstrated in the palseontological succession of the organised 

 beings on our globe. In fine, it is easy to encounter it anew by 

 grouping living beings hierarchically, from the simplest to the most 

 complex. ' It is in this triple coincidence that the grand doctrine 

 of evolution, founded by Lamarck and Darwin, finds its most 

 brilliant confirmation. 



In the animal kingdom the figurate elements can be classed in 

 two great groups : the group of the constituent elements, which 

 forms the basis, the framework of every organised being, and that of 

 the produced elements, which plays a part more or less secondary, 

 and has an existence more or less provisional. It has been ob- 

 served that the constituent elements were generally situated in 

 the interior of the body, and the produced elements on the surface. 

 But this division, to which M. Charles Robin first of all, and Mr. 

 H. Spencer afterwards, accorded a supreme importance, is only, 

 like most classifications, a commodious arrangement for grouping 

 the elements. If it were Uterally accepted — and indeed it is so 



