Chap. XIVJ SUMMARY. 265 



of the great facts in Morphology become intelligible, — 

 whether we look to the same pattern displayed by the 

 different species of the same class in their homologous 

 organs, to whatever purpose applied ; or to the serial 

 and lateral homologies in each individual animal and 

 plant. 



On the principle of successive slight variations, not 

 necessarily or generally supervening at a very early 

 period of life, and being inherited at a corresponding 

 period, we can understand the leading facts in Embry- 

 ology ; namely, the close resemblance in the individual 

 embryo of the parts which are homologous, and which 

 when matured become widely different in structure and 

 function ; and the resemblance of the homologous parts 

 or organs in allied though distinct species, though fitted 

 in the adult state for habits as different as is possible. 

 Larvae are active embryos, which have been specially 

 modified in a greater or less degree in relation to their 

 habits of life, with their modifications inherited at a 

 corresponding early age. On these same principles, — 

 and bearing in mind that when organs are reduced in 

 size, either from disuse or through natural selection, it 

 will generally be at that period of life when the being 

 has to provide for its own wants, and bearing in mind 

 how strong is the force of inheritance — the occurrence 

 of rudimentary organs might even have been anticipated. 

 The importance of embryological characters and of rudi- 

 mentary organs in classification is intelligible, on the 

 view that a natural arrangement must be genealogical. 



Finally, the several classes of facts which have been 

 considered in this chapter, seem to me to proclaim so 

 plainly, that the innumerable species, genera and 

 families, with which this world is peopled, are all 



