Xll 



A dditions arid Corrections. 



Fifth 



Sixth 



Edition. 



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Influence of fortuitous destruction on natural selection. 



On the convergence of specific forms. 



Account of the Ground- Woodpecker of La Plata modified. 



On the modification of the eye. 



Transitions through the acceleration or retardation of the 



period of reproduction. 

 The account of the electric organ of fishes added to. 

 Analogical resemblance between the eyes of Cephalopods 



and Vertebrates. 

 Claparede on the analogical resemblance of the hair-claspers 



of the Acaridae. 

 The probable use of the rattle to the Rattle-snake. 

 Helmholtz on the imperfection of the human eye. 

 The first part of this new chapter consists of portions, in a 

 much modified state, taken from chap. iv. of the former 

 editions. The latter and larger part is new, and relates 

 chiefly to the supposed incompetency of natural selection 

 to account for the incipient stages of useful structures. 

 There is also a discussion on the causes which prevent 

 in many cases the acquisition through natural selection 

 of useful structures. Lastly, reasons are given for dis- 

 believing in great and sudden modifications. Gradations 

 of character, often accompanied by changes of function, 

 are likewise here incidentally considered. 

 The statement with respect to young cuckoos ejecting their 



foster-brothers confirmed. 

 On the cuckoo-like habits of the Molothrus. 

 On fertile hybrid moths. 



The discussion on the fertility of hybrids not having been ac- 

 quired through natural selection condensed and modified. 

 On the causes of sterility of hybrids, added to and corrected. 

 Pyrgoma found in the chalk. 

 Extinct forms serving to connect existing groups. 

 On earth adhering to the feet of migratory birds. 

 On the wide geographical range of a species of Galaxias, 



a fresh-water fish. 

 Discussion on analogical resemblances, enlarged and modified. 

 Homological structure of the feet of certain marsupial 



animals. 

 On serial homologies, corrected. 

 Mr. E. Ray Lankester on morphology. 

 On the asexual reproduction of Chironomus. 

 On the origin of rudimentary parts, corrected. 

 Recapitulation on the sterility of hybrids, corrected. 

 Recapitulation on the absence of fossils beneath the Cam- 

 brian svstem, corrected. 

 Natural selection not the exclusive agency in the modi- 

 fication of species, as always maintained in this work. 

 The belief in the separate creation of species generally held 

 by naturalists, until a recent period. 



