34 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



the slow transformations admitted by Lamarck and 

 Darwin. On this hypothesis, the rapid changes of 

 the surrounding medium act by preference on the 

 embryo, and determine a somewhat sudden produc- 

 tion of new forms, just as monsters are experiment- 

 ally produced by placing embryos in abnormal 

 conditions of development. These new species, once 

 formed, will be preserved by the laws of heredity. 

 This hypothesis, the paternity of which incontest- 

 ably belongs to Geoffroy - Saint - Hilaire, has re- 

 appeared on several occasions in science under the 

 name of saltation, and has received in these latter 

 days a new form and actuality from the curious 

 botanical observations of M. Hugo de Vries. We 

 shall have to discuss it later on from the palseonto- 

 logical point of view. 



More important still from its theoretical and 

 practical consequences is the idea of which Geoffroy- 

 Saint-Hilaire had a glimpse from the comparison of 

 the adult state of inferior animals with the embry- 

 onic stages of animals in higher stages of organiza- 

 tion. The inferior animals thus appear as if they 

 had been struck by an arrest of development in the 

 realization of their initial plan. It is doubtless 

 allowable to see in these ideas of Geoffroy-Saint- 

 Hilaire the germ of the theories of parallelism be- 

 tween individual embryological development and the 

 palceontological evolution of the same animal form, a 

 fruitful theory if not carried too far, and of which 

 we shall have to show some happy applications to 

 the history of several groups of fossil animals. 



