CHAP. VIII.] LIKENESSES IN ANIMALS AND PLANTS. 263 



3. Parts which, upon the hypothesis of evolution, are 

 descendants of some ancient similar structure e.g., the arm 

 and leg bones of the horse and of the rhinoceros. 



4. Parts which are similar as to their mode of origin in 

 the individuals compared, whatever be their racial genetic 

 relations e.g., the occipital skull-bones of a panther and of 

 a perch. 



5. Parts which do not arise similarly in the individuals 

 compared, whether or not they are the descendants of cor 

 responding parts in some one common ancestral form e.g., 

 the legs of different kinds of fly these insects differing 

 strangely in their modes of attaining their adult structure. 



6. Laterally homologous parts. 



7. Vertically homologous parts. 



8. Serially homologous parts. 



(These last three kinds of homology have been already 

 sufficiently explained.) 



9. Parts of the same individual which have a certain 

 likeness and correspondence though placed at opposite ends 

 of the body e.g., buccal and anal chambers. 



10. Parts of one individual which repeat each other and 

 which radiate from a central point e.g., any two arms of a 

 star-fish. 



11. Parts which agree with each other as being successive 

 subdivisions or segments of some part or organ as of a limb 

 or insect s feeling-organ (antenna) and which are thus serial 

 homologues of a subordinate kind, or subordinate serial 

 homologues. 



12. Parts of such subordinate serial homologues, which 

 parts stand to each other in a secondary serial relation, as, 

 for example, does the root segment of the leg of a lobster to 

 the root segment of one of its swimming appendages. 



13. Parts which stand to each other in a tertiary serial re 

 lation as being annexed to such subordinate serial homologues 

 as stand to each other in a secondary serial relation. 



14. Special homologues, which are parts existing in differ 

 ent animals, but belonging to the same special skeletal eate- 



