264 Likenesses ; or^ PJdlosophical Anatomy 



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 Avhich 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 ci 

 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 

 relation, as being annexed to such subordinate serial homo- 

 logues as stand to each other in a secondary serial relation. 



14. Special homologues which are parts existing in 

 different animals, but belonging to the same special skeletal 

 category — as, e.g., the nail of a man's middle toe and the 

 hoof of a horse. 



15. General homologues, which are parts belonging to the 

 same general skeletal category — as, e.g., when we say of a 

 part that it is a Hmb, or of another that it is a rib, or of a 

 third that it is a vertebra. We may distinguish, then, 

 different kinds and degrees of relationship, which are sever- 

 ally perceived according as the mind is directed along one 

 line of inquiry or another, and whether concerning different 

 individuals or different parts of the same individual. 



