EXPLAINING THE CONTRADICTIONS. 129 



majority of the evidence, the question is asked 

 whether some valid reason cannot be given why this 

 law should in certain cases be departed from. An 

 answer is soon found in the influence of the sur- 

 roundings of the embryo, which sometimes prevent 

 the normal course from being followed. By its own 

 innate tendency the embryo would follow the line 

 of ancestral history, but while going through its de- 

 velopment it is placed under circumstances which 

 render this impossible. In such cases the history is 

 shortened, either from necessity or to cut short the 

 embryonic period, which is the period of greatest 

 helplessness. As an illustration of the principle, 

 let us consider the -ordinary earthworm (annelid). 

 Among other peculiarities, we find that its embryo 

 possesses for a long time no mouth or digestive 

 canal. This fact is in itself proof that embryology 

 may depart from past history, for the ancestors of 

 the annelid must at all times have possessed a mouth 

 and digestive tract, or they could not have lived. 

 The embryo unquestionably departs from this his- 

 tory, and a reason for it is found in a very simple 

 fact. The use of the mouth and digestive tract is 

 to supply the animal with food. But our modern 

 annelid embryo is not required to collect food, for it 

 has a supply already at hand. The egg within 

 which the embryo develops contains a large store of 

 food already prepared to enter into the body of the 

 embryo, and therefore the presence of a mouth and 

 digestive tract is unnecessary until a much later 

 period when the food is used. And not only this, but 

 the food-yolk is so bulky that it fills the whole space 



