MORPHOLOGY OF ANIMALS 



Homology may exist between similar parts of the same 

 organism, or between similar parts of different organisms; 

 the former is called General Homology, the latter Special 

 Homology. 



1. General or Meristic Homology is similarity between parts 

 which are duplicated or repeated in the same body, such 

 as arms, legs, fingers, teeth, etc. These repetitions may be 

 bilateral or serial in position, and accordingly we recognize 

 (^) Bilateral Homology {Homotypy) such as the re- 

 semblance between the right arm and the left, etc. 



{b) Serial Homology {H o7nodynamy) such as the re- 

 semblances between arms and legs, the series of fingers, 

 teeth, etc. 



2. Special Homology {Homogeny^Homophyly) is similarity 

 between corresponding parts of different organisms, such 

 as the fore-limbs of all vertebrates, the eyes of all insects, 

 etc. 



3. Homoplasy {False Homology or ''Convergence'') is ap- 

 parent resemblance but fundamental difference between 

 parts of different organisms, as for example the eyes of 

 vertebrates and cephalopods. Such superficial resemblance 

 may be attributed to the influence of similar environments 

 and needs upon fundamentally different hereditary types ; 

 that is, starting from different types these structures have 

 "converged" toward superficially similar ones. 



4. Causes of Homology. There is only one scientific explana- 

 tion of the cause of all real homolog}^, whether general or 

 special, and that is similarity of source or origin, or com- 

 mon inheritance from the same ancestors, just as the 

 fundamental resemblances of all Africans, or of other 



