222 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



is, in my opinion, altogether improbable, unless 

 we are dealing with extremely simple organisms, 

 such as bacilli or micrococci. Nature does not 

 possess, in fact, the means of varying otherwise 

 than in its dimensions a plan of structure reduced 

 to a sphere or a simple rod, and we all know that 

 bacteriologists have found themselves compelled to 

 appeal to reactions of the environment to differen- 

 tiate micro-organisms of which the monotonous 

 morphology did not lend itself to any specific 

 description. It is, therefore, strictly possible that 

 fossil animals with a very simple structure, like 

 certain Radiolaria (Monospherid0e) or Foraminifera 

 (Globigerinse), may have lent themselves to such 

 convergences, which are difficult otherwise to 

 demonstrate. 



We shall also easily recognize that certain organs 

 preserved in the fossil state, like the most simple 

 forms of the shells of the Molluscs, the scales or 

 dermic plates of the Fishes or the Reptiles, even 

 sometimes the isolated teeth of certain Mammals, 

 may succeed among distinct groups in converging 

 in a manner complete enough to deceive the 

 observer. But, when it is a question of complex 

 organisms, or even of partial structures presenting 

 a certain degree of complication, the convergences 

 produced seem always to be of a somewhat super- 

 ficial nature, limited to one or to a small number 

 of points, which cannot resist a rigorous com- 

 parison of the organization as a whole. 



This superficial appearance of convergence ap- 

 pears very clearly, especially when we deal with 

 the higher groups of fossil animals. One of the 



