REMARKS ON MR. DARWJN's THEORY. 



135 



4. Why the extinction of old forms is the almost inevitable conse- 



quence of the production of new ones. 



5. Why, when a species disappears, it never re-appears (although 



this is within the range of possibility). 



6. Why groups of species increase in number slowly, and endure 



for unequal periods of time. 



7. Why, the more ancient a form is, the more it generally differs 

 from those now living. 



8. Why all the forms of life are linked together. 



9. Why there is often great difficulty in drawing a line between 



two species. 



10. Why, as a general rule, in life on the globe there have been 



" an ascent, and progress in the main." 



11. Why the lower forms of life have larger specific existences than 

 the higher ones*. 



12. Why the older forms lived unchanged for longer periods of 

 time than the newer ones, t because they were more widely 

 distributed. 



13. Why the deep-sea shells and those of the land and fresh- water 

 enjoy a longer range in time than the littoral species ; for 

 the littoral species being confined to narrow zones in depth 

 are much more likely to suffer from elevation or subsidence 

 than those that live in the deep-sea, or on the land and in fresh- 

 water. 



14. Why some animals and plants have rudimentary, and some- 



times useless organs. 



15. Why the homologous parts, so different in the adult, are alike 

 in the embryo. 



16. Why the embryos of the higher animals resemble, at different 

 stages of their existence, the embryos of the lower animals. J 



17. Why "in their infancy the molluscous animals are more alike, 

 both in appearance and habits, than in after life . § " 



18. Why the limbs, &c, of all animals are formed on the same 

 plan. 



19. Why the flowers, branches, &c, of plants and trees are but 

 rudimentary or metamorphosed leaves. || 



20. Why animals very often resemble in colour and appearance the 

 localities which they frequent. 



21. Why in geographical distribution there are generic as well as 



specific centres. 



22. Why typical groups and species are widely distributed, while 

 aberrant forms are usually confined to small areas. 



23. Why the inhabitants of islands bear some relation to those of 

 the nearest continent. 



* Owen's Paleontology, p. 49. 

 f Anniversary Address of Professor Phillips to the Geological Society in Feb. 1860 

 J Carpenter's " Principles of Comparative Physiology," p. 95. 

 § Woodward's " Recent and Fossil Shells," p. 10. 

 || Lindley's « Elements of Botany," p. 354. 



