128 E VOL U T/ON OF TO-DA Y. 



does. Two annelids may be selected, agreeing 

 quite closely in adult anatomy, but whose develop- 

 ment shows no likeness until the latest stages are 

 reached. Of course these annelids must have had 

 practically the same past history, if the descent the- 

 ory is true, and the fact that their embryology is so 

 very different, seems at first sight to disprove that 

 the one is the re'sume' of the other. 



But upon more careful investigation it has ap- 

 peared that these seeming contradictions form per- 

 haps the strongest argument in support of the 

 hypothesis. In the first place, it has been more and 

 more evident with advancing knowledge that, al- 

 though small groups may show irregularities, as 

 a rule, embryology is in harmony with such hypo- 

 thetical history, and is as a whole a unity. The 

 same principles apply everywhere, and facts are 

 daily being brought to light showing that harmony 

 is to be the final result. So convinced have been 

 embryologists of the truth of this fundamental 

 principle, that the presence of the seeming contra- 

 dictions has caused no hesitation. They have only 

 regarded them as obstacles to be overcome. 



Method of Explaining the Contradictions. 



In most cases these contradictions have been ex- 

 plained in a satisfactory manner, though some still 

 await further discoveries before they can be made 

 clear. The general line of argument which has been 

 used to meet the difficulties is somewhat as follows : 

 Assuming the law to be that embryology should re- 

 peat past history, an assumption supported by the 



