"28 



♦o 



NATURAL SELECTION. 



[Ch. XXXVII. 



gives birth to other polyps by what is termed ' internal 



r 



gemmation, and when at length the male and female Medusse^ 



after sexual 



nnion, produce eggs 



from which the Sertu- 



larise are born^ the whole cycle of changes returns into 

 itself, just as do the metamorphoses of an insect. The same 

 may be said of certain aphides which, coming from an 

 ^gg:> give birth by gemmation to a sexual offspring, and these 

 again to others like themselves, till at length some of their 

 descendants produce perfect and winged males and females, 

 from whose union eggs proceed, and then the cycle of trans- 

 formation recommences. 



Even if there had been any indication of the Sertularia 

 and Medusa becoming each of them independent of the 

 other, this phenomenon would not afford an illustration of 

 what is usually meant by special creation, as the new form 

 would still be evolved out of the older one by descent. In 

 truth there are only as yet two rival hypotheses, between 

 which we have our choice in regard to the origin of species 



•namely, first, that of special creation and, secondly, that of 

 creation by variation and natural selection. In the next 

 four chapters I shall treat of the light thrown by the geo- 

 graphical distribution of animals and plants on the claims 

 of these two rival hypotheses to our acceptance. 



GEO 



BAR 



ro5 



GTX' 



XVV 

 >EA 



THF 

 PEL 



Geoc 



speci 



• I • 



■\vrili 



pect( 

 same 

 cinim 

 that ^ 



were 



the 



hor 



c 



se. 



on the 

 of the 

 tHo h 



Th 



th 



11 

 e 



•^AV] 



^^^ th. 



fit 



ei 



Ollc 





