THE ANNALS 



AND 



MAGAZINE OF iNATURAL HISTORY. 



[FOURTH SERIES.] 

 No. 114. JUNE 1877. 



XLIV. — On the Variability of the Species in the case of 

 certain Fishes. By Dr. Y. Fatio*. 



Several authors have of late years flemonstrated the influ- 

 ence of the surrounclin^^ medium upon organisms, and indi- 

 cated in various particulars the variability of the species. 



The struggle for existence and natural selection especially 

 are no longer subjects of doubt with many zoologists. 



A change in such or such a condition of existence almost 

 always superinduces a parallel modification in such or such 

 an organ, the mode of action of which is more or less affected ; 

 and this first translation of the external influences necessarily 

 draws after it corresponding disturbances in several other 

 pai'ts characteristic of the species. 



Darwin, in his work on the Origin of Species, gives the 

 name of correlative variation to this kind of reaction of a 

 modified part upon other corresponding parts, and demon- 

 strates sufficiently by numerous examples that the changes 

 Avhich have taken ])lace in an individual may be reproduced 

 and multiplied by heredity. Hiickel distinguishes direct or 

 immediate influences, acting upon the individual, and indirect 

 or mediate influences, Avhich only become perceptible by here- 

 dity. This latter author even devotes a whole chapter of his 

 ' ^fatural History of Creation' to this subject, under the title 

 of " Laws of Adaptation." 



* Translated by W. S. Dallas, F.L.S., from tlie ' Ribliothcque Uni- 

 vprselle : Archives des Sciences,' tome Iviii. p. l-o. 



Ann. .f- Mag. N. Hist. Ser. 4. Vol. xix. 30 



