LECTURE XV. 



SIGNIFICANCE OF MORPHOLOGY. 



Prof. Frank M. McFarland. 



I. Scope of morphology as a branch of biology. Its 

 divisions : comparative anatomy and comparative em- 

 bryology the first dealing with the structure of 

 adult forms ; the second with the structural changes 

 passed through by them in their development. Ho- 

 mology and analogy. 



II. The most important contribution which compar- 

 ative embryology has made to the science of biology 

 is the establishment of the principle that ontogeny, 

 the development of the individual, recapitulates in 

 a measure phylogeny, the development of the race. 

 Growth of this idea : 



1. At the beginning of this century the fact gener- 

 ally recognized that the higher animals pass through 

 stages in their development, during which they closely 

 resemble lower forms in their structure. 



2. Karl Ernst von Baer, 1828, recognized this as 

 a general law, but insisted that embryonic stages 

 could only be correctly compared with embryonic 

 stages, and not with adult ones. u The more different 

 two forms are, the farther back in their development 

 must one go to find similar stages." Finally con- 

 cludes that in earliest stages all animals may be 



