122 EVOLUTION OF TO-DAY. 



alizations, which have been the guiding principles of 

 embryologists ever since. Spencer contented him- 

 self with pointing out the general principles con- 

 nected with embryology in its relation to evolu- 

 tion ; and so well taken were his deductions that 

 most of them will stand to-day as he wrote them 

 twenty years' ago. Haeckel did not stop here, 

 but having recognized the underlying principles, at- 

 tempted to apply them to special cases ; and be- 

 cause his data were then scanty he was led into 

 many erroneous conclusions. He attempted at 

 that time to do more than embryologists, with all 

 their advance in knowledge, consider themselves 

 able to do to-day. 



Embryology a Repetition of Past History. 



The fundamental principle which underlies all 

 modern research in this direction, is simply the as- 

 sumption that the development of the individual 

 repeats briefly the development of the race ; that if 

 we could trace perfectly the development of any 

 animal from the egg, we should thus get an epito- 

 mized history of the development of the race to 

 which the animal in question belongs, through the 

 countless ages of the past. The great significance 

 of this assumption is at once evident. If true, it 

 gives the student, with his microscope and section 

 instrument, the opportunity of studying in the 

 laboratory the past history of animals, of discover- 

 ing thus the exact blood-relationship of animals to 

 each other, and thus explaining most of the anom- 

 alies of classification. In short, if embryology is 



