178 THE PATH OF DEGENERATIVE EVOLUTION 



Before describing and discussing the special facts 

 to which they apply their theory, it is necessary to 

 examine its biological foundation. 



CHAPTEE I 



THE PATH OF DEGENERATION IN BIOLOGY 



WE have now to consider if the degeneration of 

 organs retraces the steps taken in their progres- 

 sive evolution. According to Hughlings Jackson 

 and Eibot, in the cases mentioned in the preceding 

 chapter, degeneration proceeds by successive atro- 

 phies occurring in the order opposite to that of 

 ontological formation. Is the same order to be 

 found when we compare the degeneration of 

 organs or of individuals with their phylogenetic 

 development ? To answer this question, we must 

 employ both morphology and embryology. Using 

 the morphological method, we shall study the re- 

 duction of a homologous organ in several species 

 descended from the same type, and compare the 

 different stages of reduction with the different 

 stages of phylogenetic development of the organ. 1 



1 In this investigation it will be necessary to compare absolutely 

 identical organs for instance, not to compare the pineal eye with 

 the paired eyes. It will be necessary also to choose animals of 

 common parentage to avoid, for instance, comparing a Vertebrate 

 eye with a Crustacean eye. 



