400 Studies in the Theory of Descent. 



successively attempted are by no means identical, 

 although closely related, since it is quite con- 

 ceivable that the first may be answered by there 

 being no precise correlation of form, or only an 

 extremely small correlation, between the caterpillar 

 and the imago, whilst, at the same time, it would 

 not be thereby decided whether the phyletic 

 development of the two stages had kept pace 

 uniformly or not. A perfect congruence of mor- 

 phological relationships could only take place if 

 transformations resulted from an internal power 

 instead of external influences. The question : 

 Does there exist a fixed correlation of form 

 between the two stages ? must therefore be 

 followed by another : Do the form-relationships 

 of the two stages coincide or not has their 

 phyletic development been uniform or not ? 



