INTRODUCTION XV 



and comparative anatomical evidence conflict with one another, the 

 difficulties of interpretation are enhanced and morphological opinion is 

 likely to be divided. Where evidence conflicts, there is no criterion by 

 which the more reliable clues may be recognized. Anatomists tend to 

 value anatomical evidence more highly; embryologists favor ontogenetic 

 evidence. In such matters, personal opinion looms large. Frequent 

 differences of opinion among morphologists have given the impression 

 that phylogenetic conclusions are exceptionally speculative and uncertain. 

 Much of this divergence, however, is due to lack of sufficient evidence. 

 The history of morphology shows that with increasing knowledge there 

 has been an increase of agreement on controverted issues. As the recent 

 upheaval in theoretical physics has shown, speculation is not peculiar 

 to morphology. Even if it be admitted that the methods of the morpholo- 

 gist resemble those of Sherlock Holmes, this similarity does not invalidate 

 his conclusions. 



