SEX AND SEXUAL CHARACTERS 473 



hermit-crab ; while in such cases as the degeneration of the eyes 

 in the blind-fish of the Kentucky caves, or the divided eyes of 

 Anableps— the fish which swims with its eyes half out of water — 

 although there is no actual change of conditions in the individual 

 lifetime, the original condition of the organ is more or less 

 completely developed first, and then the new adaptive modifica- 

 tion gradually takes place. On the other hand, we have 

 characters which obviously arose as mutations — the characters 

 the Mendelians investigate — which develop directly from the 

 ovum, and have nothing to do with adaptation, or if they are 

 ever of use to the possessor, are so only by accident. Ex- 

 amples of these are seen in the doubling of flowers, in albinism, 

 in the extra toe in certain breeds of fowls and other cases of 

 polydactylism, in the rose, pea, and walnut combs of fowls, 

 and in all the numerous characters which distinguish the 

 varieties of animals and plants under domestication, which 

 (according to my views) are of the same kind as the characters 

 which distinguish species in nature. 



References 



(i) Bateson, Mendel's Principles of Heredity, Cambridge, 1909. 



(2) SHATTOCK and Seligmann, True Hermaphroditism in the Domestic Fowl, 



Trans. Path. Soc. vol. lvii. 1906. 



(3) On the Acquirement of Secondary Sexual Characters, etc. Proc. Roy. Soc. 



London, vol. lxxiii. 1904. 



(4) Cunningham, Reproductive Elements in Myxine glutinosa, Quart. Journ. 



Mic. Sci. 1887. 



(5) Schreiner, Ueber das Generationsorgan von Myxine glutinosa, Biol. 



Centralbl. bd. xxiv. 1904. 



(6) Lane Claypon, Proc. Roy. Soc. London, vol. lxxiii. 1904. 



(7) Bayliss and Starling, Chemische Koordination der Funtionen des Korpers, 



Ergeb. der Physiol, v. Jahrgang, 1906. 



(8) Cunningham, Heredity of Secondary Sexual Characters in relation to 



Hormones, Archiv fiir Entiuicklungsmechanik, bd. xxvi. 1908. 



(9) Starling and Lane Claypon, Factors which determine the Growth and 



Activity of the Mammary Glands, Proc. Roy. Soc. London, vol. Ixxvii. 

 1906. 



(10) NUSSBAUM, Innere Secretion und Nerveneinfiuss, Ergebnisse der Anatomie u. 



Entivicklungsgesch. bd. xv. 1905 



